Updates for CI

Author: Piinks

dev/bots/check_tests_cross_imports.dart

@@ -167,8 +167,7 @@ class TestsCrossImportChecker {
   ///    Widgets tests importing Material or Cupertino.
   // TODO(justinmc): Fix all of these tests so there are no cross imports.
   // See https://github.com/flutter/flutter/issues/177028.
-  static final Set<String> knownCupertinoCrossImports = <String>{
-  };
+  static final Set<String> knownCupertinoCrossImports = <String>{};
 
   static final Set<String> _knownCrossImports = knownWidgetsCrossImports.union(
     knownCupertinoCrossImports,

dev/bots/test/check_tests_cross_imports_test.dart

@@ -127,6 +127,9 @@ void main() {
   });
 
   test('when not all cupertino knowns have cross imports', () async {
+    if (TestsCrossImportChecker.knownCupertinoCrossImports.isEmpty) {
+      return;
+    }
     final String excluded = TestsCrossImportChecker.knownCupertinoCrossImports.first;
     buildTestFiles(excludes: <String>{excluded});
     bool? success;