fix(flutter/test): testWidgets skip takes bool, not String

CI analyze flagged storage_section_test.dart's `skip: _skipDrift` calls.
testWidgets has signature `skip: bool?`; only test() takes `String?` as
the skip-reason. Changed _skipDrift in this file to `const bool = true`
and moved the rationale into a comment. The other two drift-cohort
files (sync_controller_test, audio_cache_manager_test) use test() so
their String const is fine.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/test/settings/storage_section_test.dart

@@ -17,7 +17,11 @@ class _MockStorage extends Mock implements FlutterSecureStorage {}
 // which opens the AppDb via NativeDatabase. CI's flutter-ci runner
 // lacks libsqlite3.so so this silently emits a warning today and would
 // break under stricter analyze. Skipped with the drift cohort.
-const _skipDrift = 'libsqlite3 missing on flutter-ci runner; on-device covers';
+//
+// testWidgets only accepts a bool for skip (unlike test() which takes
+// a String reason). Reason: 'libsqlite3 missing on flutter-ci runner;
+// on-device covers'. See Fable #399.
+const _skipDrift = true;
 
 void main() {
   setUpAll(() {