Fix potential memory leaks.

[maciejwalkowiak]

📜 Description

Fix potential memory leaks - happening either when Sentry works in servlet environment on application undeployment - or when more than one integration is active.

💚 How did you test it?

Running a sample application. I am not sure if there is a way to write a test for that.

📝 Checklist

• I reviewed the submitted code
• I added tests to verify the changes
• I updated the docs if needed
• No breaking changes

[codecov-commenter]

Codecov Report

Merging #1909 (aa35889) into main (33bdce3) will increase coverage by 0.03%.
The diff coverage is 92.30%.

@@             Coverage Diff              @@
##               main    #1909      +/-   ##
============================================
+ Coverage     75.42%   75.46%   +0.03%     
- Complexity     2244     2248       +4     
============================================
  Files           225      225              
  Lines          8026     8037      +11     
  Branches        852      852              
============================================
+ Hits           6054     6065      +11     
  Misses         1562     1562              
  Partials        410      410              

Impacted Files	Coverage Δ
...ry/src/main/java/io/sentry/MainEventProcessor.java	82.40% <0.00%> (ø)
.../io/sentry/spring/SentryInitBeanPostProcessor.java	97.67% <100.00%> (+0.45%)	⬆️
sentry/src/main/java/io/sentry/HostnameCache.java	90.69% <100.00%> (+0.69%)	⬆️
sentry/src/main/java/io/sentry/Sentry.java	42.28% <100.00%> (+0.38%)	⬆️

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