Bump Dartdoc to 8.0.2 (#139780)

Bumping DartDoc to 8.0.2. https://pub.dev/packages/dartdoc/changelog#802

Made a fix for https://github.com/flutter/flutter/issues/139755, so this
release rolls that fix in.
The fix was made here https://github.com/dart-lang/dartdoc/pull/3595.

Not sure who's most relevant to tag so ccing some folks.
cc. @srawlins @jason-simmons @gspencergoog 

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we expect every widget to implement].
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- [X] 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].
- [x] All existing and new tests are passing.

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dev/bots/docs.sh

@@ -111,7 +111,7 @@ function generate_docs() {
     # Install and activate dartdoc.
     # When updating to a new dartdoc version, please also update
     # `dartdoc_options.yaml` to include newly introduced error and warning types.
-    "$DART" pub global activate dartdoc 8.0.0
+    "$DART" pub global activate dartdoc 8.0.2
 
     # Install and activate the snippets tool, which resides in the
     # assets-for-api-docs repo: