ci: use serial GC instead of parallel

Author: triceo

src/main/java/ai/timefold/solver/benchmarks/micro/common/AbstractMain.java

@@ -178,7 +178,7 @@ public ChainedOptionsBuilder getBaseJmhConfig(C configuration) {
                 .forks(configuration.getForkCount())
                 .warmupIterations(configuration.getWarmupIterations())
                 .measurementIterations(configuration.getMeasurementIterations())
-                .jvmArgs("-XX:+UseParallelGC", "-Xmx2g") // Stable, predictable GC pause times.
+                .jvmArgs("-XX:+UseSerialGC", "-Xmx2g") // Throughput-focused GC.
                 .result(resultsDirectory.resolve("results.json").toAbsolutePath().toString())
                 .resultFormat(ResultFormatType.JSON)
                 .shouldDoGC(true);