Set 4 threads to run CTest on Android devices (match number of little cores) (#9372)

build_tools/buildkite/cmake/android/arm64-v8a/pipeline.yml

diff --git a/build_tools/buildkite/cmake/android/arm64-v8a/pipeline.yml b/build_tools/buildkite/cmake/android/arm64-v8a/pipeline.yml
index 0212f26..47415c3 100644
--- a/build_tools/buildkite/cmake/android/arm64-v8a/pipeline.yml
+++ b/build_tools/buildkite/cmake/android/arm64-v8a/pipeline.yml
@@ -26,7 +26,7 @@
       - "tar xzf build-artifacts.tgz"
       - "find build-android/ -name '*.cmake' -exec sed -i \"s!\\$IREE_DOCKER_WORKDIR/!\\$PWD/!g\" {} \\;"
       - "cd build-android/"
-      - "ctest --timeout 900 --output-on-failure"
+      - "ctest -j 4 --timeout 900 --output-on-failure"
     agents:
       - "android-soc=google-tensor"
       - "queue=test-android"
@@ -44,7 +44,7 @@
       - "cd build-android/"
       # Pixel 4 ships an old Adreno GPU driver. There are quite a few bugs triggered by our tests.
       # Disable running tests entirely on Pixel 4. Moto Edge X30 gets us covered on Adreno GPU.
-      - "ctest --timeout 900 --output-on-failure --label-exclude \"vulkan\""
+      - "ctest -j 4 --timeout 900 --output-on-failure --label-exclude \"vulkan\""
     agents:
       - "android-soc=snapdragon-855"
       - "queue=test-android"
@@ -60,7 +60,7 @@
       - "tar xzf build-artifacts.tgz"
       - "find build-android/ -name '*.cmake' -exec sed -i \"s!\\$IREE_DOCKER_WORKDIR/!\\$PWD/!g\" {} \\;"
       - "cd build-android/"
-      - "ctest --timeout 900 --output-on-failure"
+      - "ctest -j 4 --timeout 900 --output-on-failure"
     agents:
       - "android-soc=snapdragon-8gen1"
       - "queue=test-android"