Increase test concurrency on internal bots

Bug: 297302759
Change-Id: I850a11c8e52d87c280e593cac1dd880288f6b7b4
diff --git a/tools/internal_test.py b/tools/internal_test.py
index b32c378..848edac 100755
--- a/tools/internal_test.py
+++ b/tools/internal_test.py
@@ -384,7 +384,7 @@
   log('Running once with hash %s' % git_hash)
   env = os.environ.copy()
   # Bot does not have a lot of memory.
-  env['R8_GRADLE_CORES_PER_FORK'] = '8'
+  env['R8_GRADLE_CORES_PER_FORK'] = '5'
   failed = any([execute(cmd, archive, env) for cmd in TEST_COMMANDS])
   # Gradle daemon occasionally leaks memory, stop it.
   gradle.RunGradle(['--stop'])