bump: logback-classic 1.5.15 (was 1.5.12) #1527

Job	Run time
Gradle tests	10m 23s
Compile Benchmarks	5m 24s
Compile and test (2.13)	8m 11s
Checks	6m 0s
Maven tests	9m 39s
Compile and test (3.3)	8m 50s
sbt scripted tests (gen-scala-server, 2.13)	11m 15s
sbt scripted tests (gen-java, 2.13)	7m 40s
sbt scripted tests (scala-2_13, 2.13)	6m 57s
sbt scripted tests (scala3, 3.3)	7m 2s
	1h 21m 21s

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