License update - Batch 48

[mossmana]

Updates the license headers for:

1. packages/devtools_app/web/index.html
2. packages/devtools_app/web/styles.css
3. packages/devtools_app/web/unsupported-browser.html

#8216

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.