fix: 'SentryFileManager+Test.h' file not found

[brustolin]

📜 Description

The pr #3929 introduced a bug that happens when Sentry is added with cocoapod, by exposing a Test file during debug, but this file is not available for cocoapod.

💚 How did you test it?

Sample

📝 Checklist

You have to check all boxes before merging:

• I reviewed the submitted code.
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

[krystofwoldrich]

LGTM 🚀

Fixes getsentry/sentry-react-native#3802 (review)

Tested with the RN Repo Sample

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.810%. Comparing base (3c58bf9) to head (d307a37).

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #3950       +/-   ##
=============================================
+ Coverage   90.766%   90.810%   +0.043%     
=============================================
  Files          588       588               
  Lines        45878     45879        +1     
  Branches     16368     16353       -15     
=============================================
+ Hits         41642     41663       +21     
+ Misses        4166      4146       -20     
  Partials        70        70               

Files	Coverage Δ
Sources/Sentry/SentryTracer.m	97.607% <ø> (+0.717%)	⬆️

... and 9 files with indirect coverage changes

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