chore(build): fix formatting of JVM arguments in gradle.properties

[wmontwe]

This should resolve the issue with: https://github.com/thunderbird/thunderbird-android/actions/runs/26045608112/job/76568868743

java.nio.charset.IllegalCharsetNameException: UTF-8,-XX:+UseG1GC,-XX:SoftRefLRUPolicyMSPerMB=1,-XX:ReservedCodeCacheSize=512m,-XX:InitialCodeCacheSize=256m,-XX:+HeapDumpOnOutOfMemoryError,-Xmx8g,-XX:+IgnoreUnrecognizedVMOptions,-XX:+SuppressCDSWarning

[github-actions]

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