Fix wrong default environment in Session

[lbloder]

📜 Description

The environment getter in SentryOptions now returns "production" as default if not set.

💡 Motivation and Context

Fixes #2381

💚 How did you test it?

📝 Checklist

• 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

[github-actions]

	Messages
📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

Generated by 🚫 dangerJS against 4ed1f71

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	331.45 ms	399.00 ms	67.55 ms
Size	1.73 MiB	2.26 MiB	547.63 KiB

Previous results on branch: feat/default_environment

Startup times

Revision	Plain	With Sentry	Diff
fe1d2d7	328.68 ms	385.94 ms	57.26 ms
1dd523f	387.79 ms	423.14 ms	35.35 ms

App size

Revision	Plain	With Sentry	Diff
fe1d2d7	1.73 MiB	2.26 MiB	547.63 KiB
1dd523f	1.73 MiB	2.26 MiB	547.63 KiB

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01 ⚠️

Comparison is base (db18794) 81.31% compared to head (4ed1f71) 81.31%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2610      +/-   ##
============================================
- Coverage     81.31%   81.31%   -0.01%     
  Complexity     4187     4187              
============================================
  Files           336      336              
  Lines         15486    15485       -1     
  Branches       2021     2020       -1     
============================================
- Hits          12592    12591       -1     
  Misses         2101     2101              
  Partials        793      793              

Impacted Files	Coverage Δ
...ry/src/main/java/io/sentry/MainEventProcessor.java	85.41% <100.00%> (-0.11%)	⬇️
sentry/src/main/java/io/sentry/SentryOptions.java	80.43% <100.00%> (ø)

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