Prefer Minitest's location for test failures.

When running tests, the Rails test runner would report the start of the test method as the test failure.

For this test:

```ruby
1 require 'test_helper
2
3 class BunnyTest < ActiveSupport::TestCase
4   test "something failing" do
5     assert false, 'This failed'
6   end
7 end
```

The runner outputs 5 instead of 4:

```
............................................F

This failed

bin/rails test test/models/bunny_test.rb:5

........
```

railties/lib/rails/test_unit/reporter.rb

@@ -57,8 +57,14 @@ def fail_fast?
       end
 
       def format_rerun_snippet(result)
-        location, line = result.method(result.name).source_location
-        "#{self.executable} #{relative_path_for(location)}:#{line}"
+        # Try to extract path to assertion from backtrace.
+        if result.location =~ /\[(.*)\]\z/
+          assertion_path = $1
+        else
+          assertion_path = result.method(result.name).source_location.join(':')
+        end
+
+        "#{self.executable} #{relative_path_for(assertion_path)}"
       end
   end
 end

railties/test/application/test_runner_test.rb

@@ -344,7 +344,7 @@ def test_output_inline_by_default
       create_test_file :models, 'post', pass: false
 
       output = run_test_command('test/models/post_test.rb')
-      assert_match %r{Running:\n\nPostTest\nF\n\nwups!\n\nbin/rails test test/models/post_test.rb:4}, output
+      assert_match %r{Running:\n\nPostTest\nF\n\nwups!\n\nbin/rails test test/models/post_test.rb:6}, output
     end
 
     def test_only_inline_failure_output