Fix build failure

[mossmana]

As a result of an automated search/replace of license headers for ongoing work for #8216, devtools/tools/release_build.sh had been corrupted. This caused a failure at build time.

https://ci.chromium.org/ui/p/dart-internal/builders/flutter/devtools/1199/overview

This PR is an attempt to fix the build failure.

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read the [Flutter Style Guide] recently, and have followed its advice.
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or there is a reason for not adding tests.