[jvm] duplicated filename creates exceptions when updating snapshot

There is a possible issue that I encountered with duplicated file names of tests. (in different packages). The assertion was marked for overwrite with `toBe_TODO()` and the following exception was thrown:
```
[com.diffplug.selfie.junit5.SelfieTestExecutionListener] threw exception for method: testPlanExecutionFinished(org.junit.platform.launcher.TestPlan@65b49da9) java.lang.AssertionError: Expected to find inline assertion on line ...
```
With some debugging i found that there was a file with a identical name red with different content instead of the correct one, before the exception was thrown.

Also I'm not sure if this a known limitation or a bug

Start by reproducing the snapshot update with tests that use the same filename in different packages. Trace how snapshot files are selected and how inline assertions are located when testPlanExecutionFinished runs. Done means duplicate filenames resolve to the correct content and the overwrite assertion completes without the reported exception.

Written by the indexing model from the issue text.