Co-authored-by: Alexander Dahlberg <alexander.dahlberg@sigma.se>

Fixes test/animation/animation_controller_test.dart in #85160

Problem:
The test 'animateTo can deal with duration == Duration.Zero' was failing with the following error:

Expected: <0>
Actual: <5>
Expected no animation.
package:test_api expect
package:flutter_test/src/widget_tester.dart 484:3 expect
test/animation/animation_controller_test.dart 511:5 main.

Following line finds 5 transientCallbacks scheduled, while expecting zero, if shuffled with seed 123:

expect(SchedulerBinding.instance!.transientCallbackCount, equals(0), reason: 'Expected no animation.');

This is caused by some other test leaving transientCallbacks scheduled.

Fix:
By disposing the AnimationController after each test, the transientCallbacks get cleaned up.
I chose to dispose all controllers in every test, to make sure there is no risk of leaks.