Bump src/external/tinyxml2 from c2d3087 to 321ea88

Bumps [src/external/tinyxml2](https://github.com/leethomason/tinyxml2) from `c2d3087` to `321ea88`.
- [Release notes](https://github.com/leethomason/tinyxml2/releases)
- [Commits](leethomason/tinyxml2@c2d3087...321ea88)

---
updated-dependencies:
- dependency-name: src/external/tinyxml2
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>