Describe the bug

#5780 (comment) explains the specifics in detail, but essentially it's possible for the code coverage script to incorrectly miss files whose tests are either missing or in the wrong directory.

Steps To Reproduce

Either move a test to the wrong directory (like the one mentioned in #5780) or find one, and modify it to have a change. Then, run the incremental code coverage process and verify that the test wasn't run.

Expected Behavior

Files with tests that aren't exempted and essentially missing (due to being in the wrong test directory) should trigger an incremental code coverage failure so that it's impossible to check in a broken test as happened in #5780.

Screenshots/Videos

No response

What device/emulator are you using?

No response

Which Android version is your device/emulator running?

No response

Which version of the Oppia Android app are you using?

No response

Additional Context

#5780 has significant context on where this issue is found, and possible mitigations.