BE: Fix NPE on ptotobuf tests on Windows due to path separator mismatch

[DimaVilda]

Issue submitter TODO list

• I've looked up my issue in FAQ
• I've searched for an already existing issues here
• I've tried running main-labeled docker image and the issue still persists there
• I'm running a supported version of the application which is listed here

Describe the bug (actual behavior)

1. Run protobuf related tests on Windows OS ( i.e. ProtobufFileSerdeTest)
2. See multiple NPEs on each test case related to incorrect 'language/language.proto' file location

Expected behavior

All tests should pass on Windows OS

Your installation details

Build and run current master branch.

Steps to reproduce

Build kafka-ui and run ProtobufFileSerdeTest. See NPE

Screenshots

Logs

No response

Additional context

No response

[github-actions]

Hi DimaVilda! 👋

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[DimaVilda]

hey team
I'd like to be assigned to this issue since I already investigated the problem. However anybody can also take it also

[Haarolean]

Once square/wire#3215 is closed, a method from #723 can be nuked