Upgrade to java 21

[Sheikah45]

No description provided.

[codecov]

Codecov Report

Merging #3064 (bece543) into develop (7e39b73) will decrease coverage by 0.16%.
Report is 2 commits behind head on develop.
The diff coverage is 62.51%.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #3064      +/-   ##
=============================================
- Coverage      58.88%   58.72%   -0.16%     
+ Complexity      4461     4460       -1     
=============================================
  Files            558      560       +2     
  Lines          20201    20451     +250     
  Branches        1035     1035              
=============================================
+ Hits           11895    12010     +115     
- Misses          7757     7896     +139     
+ Partials         549      545       -4     

Files	Coverage Δ
...client/achievements/AchievementItemController.java	100.00% <ø> (ø)
.../main/java/com/faforever/client/api/IceServer.java	100.00% <100.00%> (ø)
.../java/com/faforever/client/audio/AudioService.java	100.00% <100.00%> (ø)
...ava/com/faforever/client/avatar/AvatarService.java	100.00% <100.00%> (+18.18%)	⬆️
...orever/client/chat/ChatCategoryItemController.java	65.51% <100.00%> (-0.59%)	⬇️
...ava/com/faforever/client/chat/ChatChannelUser.java	93.93% <100.00%> (+4.75%)	⬆️
...om/faforever/client/chat/TrustEveryoneFactory.java	25.00% <ø> (ø)
...r/client/chat/UserListCustomizationController.java	100.00% <ø> (ø)
...ever/client/chat/emoticons/EmoticonController.java	100.00% <ø> (ø)
...lient/chat/emoticons/EmoticonsGroupController.java	100.00% <ø> (ø)
... and 193 more

... and 22 files with indirect coverage changes

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