Update kotlin to v1.9.21

[juul-mobile-bot]

This PR contains the following updates:

Package	Type	Update	Change
org.jetbrains.kotlin.plugin.serialization	plugin	patch	1.9.20 -> 1.9.21
org.jetbrains.kotlin.multiplatform	plugin	patch	1.9.20 -> 1.9.21
org.jetbrains.kotlin.js	plugin	patch	1.9.20 -> 1.9.21

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Warning

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[codecov]

Codecov Report

Attention: 18 lines in your changes are missing coverage. Please review.

Comparison is base (56a59f1) 57.25% compared to head (b8fc492) 57.97%.
Report is 154 commits behind head on main.

Files	Patch %	Lines
koap/src/commonMain/kotlin/Message.kt	33.33%	12 Missing ⚠️
koap/src/commonMain/kotlin/Debug.kt	25.00%	3 Missing ⚠️
koap/src/commonMain/kotlin/Decoder.kt	66.66%	2 Missing ⚠️
koap/src/commonMain/kotlin/ByteArrayReader.kt	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #227      +/-   ##
============================================
+ Coverage     57.25%   57.97%   +0.71%     
  Complexity       11       11              
============================================
  Files             8        8              
  Lines           613      652      +39     
  Branches        145      144       -1     
============================================
+ Hits            351      378      +27     
- Misses          223      235      +12     
  Partials         39       39              

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