Add changlog entry for 3.38.8

[reidbaker]

• Add changlog entry for 3.38.8

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 and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• 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 this PR is [test-exempt].
• I followed the [breaking change policy] and added [Data Driven Fixes] where supported.
• All existing and new tests are passing.

[flutter-dashboard]

This pull request was opened from and to a release candidate branch. This should only be done as part of the official Flutter release process. If you are attempting to make a regular contribution to the Flutter project, please close this PR and follow the instructions at Tree Hygiene for detailed instructions on contributing to Flutter.

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[fluttergithubbot]

An existing Git SHA, 98a6d3ec7186cdc659f14dd7fc90cc7153f0de26, was detected, and no actions were taken.

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[gemini-code-assist]

Code Review

This pull request adds a changelog entry for the 3.38.8 hotfix. The review found a minor formatting issue in CHANGELOG.md where the new version header uses an incorrect markdown level. A suggestion has been provided to fix this for consistency with the rest of the file.

[gemini-code-assist]

The markdown header for the new version should be level 3 (###) to maintain consistency with other hotfix entries in this file. The current level 2 (##) is typically used for major version change sections (e.g., ## Flutter 3.38 Changes).

Suggested change

	## [3.38.8](https://github.com/flutter/flutter/releases/tag/3.38.8)
	### [3.38.8](https://github.com/flutter/flutter/releases/tag/3.38.8)

[jtmcdole]

This was actually correctly called out.