Devtools announcement has text that has a background that is difficult to read

### Steps to reproduce

1. Create a new app on flutter v 3.44 or after.
2. Open devtools
3. The announcement will be shown on the right hand side of the devtools with hard to read text due to the background color.

### Expected results

The display text for the release notes header text should be eligible and accessible.

### Actual results

Currently, there is a background color added to the devtools announcement that makes it hard to read.

### Code sample

N/A

### Screenshots or Video

### Logs

N/A

### Flutter Doctor output

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.44.5, on macOS 26.5.2 25F84 darwin-arm64, locale en)
[✓] Android toolchain - develop for Android devices (Android SDK version 36.1.0)
[✓] Xcode - develop for iOS and macOS (Xcode 26.1)
[✓] Chrome - develop for the web
[✓] Connected device (4 available)
[✓] Network resources

• No issues found!

Reproduce the announcement in DevTools with Flutter 3.44 or later and inspect the release-notes header where the text/background contrast is applied. Compare the rendered text against the expected accessible presentation; done means the header is readable and its contrast meets accessibility expectations.

Written by the indexing model from the issue text.