test(perf): avoid OOM while running big batches of commit tests

TIL that you can still kill a machine with 64GB+64GB RAM+Swap if
you run enough Kotlin on it. Thanks gradle.

tools/test-commits.sh

@@ -14,6 +14,7 @@ first_commit="$1"
 while :; do
     echo "testing $(git log --pretty=oneline -1)"
     ./gradlew -q clean uninstallPlayDebug jacocoTestReport :api:lintRelease :AnkiDroid:lintPlayRelease ktlintCheck
+    ./gradlew --stop
     [ $(git rev-parse HEAD) = $first_commit ] && break
     git checkout HEAD^
 done