Use ActiveSupport::TestCase for Tracker tests

[skipkayhil]

Minitest::Test does not support all of the same options as ActiveSupport::TestCase, such as running bin/test : and -n /regex/. Trying to use these options on this file would just run all of the Minitest::Tests no matter what options were passed.

This commit fixes the ability to use those options by using ActiveSupport::TestCase (like every other test in the repo).

Before:

$ bin/test test/template/dependency_tracker_test.rb:217
Running 59 tests in parallel using 8 processes
Run options: --seed 42725

.........................................................

Finished in 0.322759s, 176.6024 runs/s, 176.6024 assertions/s.
57 runs, 57 assertions, 0 failures, 0 errors, 0 skips

After:

$ bin/test test/template/dependency_tracker_test.rb:217
Running 59 tests in parallel using 8 processes
Run options: --seed 15213

...

Finished in 0.359162s, 8.3528 runs/s, 8.3528 assertions/s.
3 runs, 3 assertions, 0 failures, 0 errors, 0 skips