Bump extern/amrex from 6d9c25b to b9d549b (#786)

Bumps [extern/amrex](https://github.com/AMReX-Codes/amrex) from
`6d9c25b` to `b9d549b`.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/AMReX-Codes/amrex/commit/b9d549bcf4a6e035e6050c92083d42a30a4078b1"><code>b9d549b</code></a>
Add option to do stable redistribute with GPUs (<a
href="https://redirect.github.com/AMReX-Codes/amrex/issues/4200">#4200</a>)</li>
<li><a
href="https://github.com/AMReX-Codes/amrex/commit/47108f00fadae9c72704e086c8d0a5881c20456a"><code>47108f0</code></a>
Fix typo in documentation of Tensor Linear Solver (<a
href="https://redirect.github.com/AMReX-Codes/amrex/issues/4206">#4206</a>)</li>
<li><a
href="https://github.com/AMReX-Codes/amrex/commit/92679babfc2cc66ca06ee591a80001db57c89878"><code>92679ba</code></a>
Remove HIP_INDIRECT_FUNCTION (<a
href="https://redirect.github.com/AMReX-Codes/amrex/issues/4199">#4199</a>)</li>
<li><a
href="https://github.com/AMReX-Codes/amrex/commit/dc745bbddfef07c79da6299a52ab354d1c423cf6"><code>dc745bb</code></a>
Use The_Comms_Arena in particle communication. (<a
href="https://redirect.github.com/AMReX-Codes/amrex/issues/4175">#4175</a>)</li>
<li><a
href="https://github.com/AMReX-Codes/amrex/commit/c0602940a47c11b7e0b7bb753067f504fefe3660"><code>c060294</code></a>
Refactor grid-stride loop (<a
href="https://redirect.github.com/AMReX-Codes/amrex/issues/4190">#4190</a>)</li>
<li><a
href="https://github.com/AMReX-Codes/amrex/commit/8f4fbaf3204af0ede5ed21ce7de176f0f45486a9"><code>8f4fbaf</code></a>
Fix a typo in CI build option (<a
href="https://redirect.github.com/AMReX-Codes/amrex/issues/4196">#4196</a>)</li>
<li><a
href="https://github.com/AMReX-Codes/amrex/commit/0c7df10b24b8a82f6de96292282a8833e0f9ebd8"><code>0c7df10</code></a>
STL optimization: Bounding volume hierarchy (<a
href="https://redirect.github.com/AMReX-Codes/amrex/issues/4140">#4140</a>)</li>
<li><a
href="https://github.com/AMReX-Codes/amrex/commit/c333708d59f01ab664363ba426e85ad24c1fb23d"><code>c333708</code></a>
Bounded sampling (<a
href="https://redirect.github.com/AMReX-Codes/amrex/issues/4195">#4195</a>)</li>
<li><a
href="https://github.com/AMReX-Codes/amrex/commit/b00c828b78e3a6036759d5a1408a4796ee2ba97f"><code>b00c828</code></a>
amrex::FFT (<a
href="https://redirect.github.com/AMReX-Codes/amrex/issues/4193">#4193</a>)</li>
<li><a
href="https://github.com/AMReX-Codes/amrex/commit/62c2a81eac7862d526e5861ef2befc00b7f5b759"><code>62c2a81</code></a>
SmallMatrix: Structured binding support (<a
href="https://redirect.github.com/AMReX-Codes/amrex/issues/4189">#4189</a>)</li>
<li>Additional commits viewable in <a
href="https://github.com/AMReX-Codes/amrex/compare/6d9c25b989f19eaccbc561db8f2e3affe587bff7...b9d549bcf4a6e035e6050c92083d42a30a4078b1">compare
view</a></li>
</ul>
</details>
<br />


Dependabot will resolve any conflicts with this PR as long as you don't
alter it yourself. You can also trigger a rebase manually by commenting
`@dependabot rebase`.

[//]: # (dependabot-automerge-start)
[//]: # (dependabot-automerge-end)

---

<details>
<summary>Dependabot commands and options</summary>
<br />

You can trigger Dependabot actions by commenting on this PR:
- `@dependabot rebase` will rebase this PR
- `@dependabot recreate` will recreate this PR, overwriting any edits
that have been made to it
- `@dependabot merge` will merge this PR after your CI passes on it
- `@dependabot squash and merge` will squash and merge this PR after
your CI passes on it
- `@dependabot cancel merge` will cancel a previously requested merge
and block automerging
- `@dependabot reopen` will reopen this PR if it is closed
- `@dependabot close` will close this PR and stop Dependabot recreating
it. You can achieve the same result by closing it manually
- `@dependabot show <dependency name> ignore conditions` will show all
of the ignore conditions of the specified dependency
- `@dependabot ignore this major version` will close this PR and stop
Dependabot creating any more for this major version (unless you reopen
the PR or upgrade to it yourself)
- `@dependabot ignore this minor version` will close this PR and stop
Dependabot creating any more for this minor version (unless you reopen
the PR or upgrade to it yourself)
- `@dependabot ignore this dependency` will close this PR and stop
Dependabot creating any more for this dependency (unless you reopen the
PR or upgrade to it yourself)


</details>

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>