CI: test 4 workers on arm64 pandas-dev#36719

Author: fangchenli

.travis.yml

@@ -37,13 +37,13 @@ matrix:
   include:
     - arch: arm64
       env:
-        - JOB="3.7, arm64" PYTEST_WORKERS=auto ENV_FILE="ci/deps/travis-37-arm64.yaml" PATTERN="(not slow and not network and not clipboard and not arm_slow)"
+        - JOB="3.7, arm64" PYTEST_WORKERS=4 ENV_FILE="ci/deps/travis-37-arm64.yaml" PATTERN="(not slow and not network and not clipboard and not arm_slow)"
 
   allow_failures:
     # Moved to allowed_failures 2020-09-29 due to timeouts https://github.com/pandas-dev/pandas/issues/36719
     - arch: arm64
       env:
-        - JOB="3.7, arm64" PYTEST_WORKERS=auto ENV_FILE="ci/deps/travis-37-arm64.yaml" PATTERN="(not slow and not network and not clipboard and not arm_slow)"
+        - JOB="3.7, arm64" PYTEST_WORKERS=4 ENV_FILE="ci/deps/travis-37-arm64.yaml" PATTERN="(not slow and not network and not clipboard and not arm_slow)"
 
 
 before_install: