move 3.9 travis build to allowed failuresss (#34894)

Author: jreback

.travis.yml

@@ -69,9 +69,9 @@ matrix:
       env:
         - JOB="3.7, arm64" PYTEST_WORKERS=8 ENV_FILE="ci/deps/travis-37-arm64.yaml" PATTERN="(not slow and not network and not clipboard)"
     - dist: bionic
-      python: 3.9-dev
       env:
-        - JOB="3.9-dev" PATTERN="(not slow and not network)"
+        - JOB="3.9-dev" PATTERN="(not slow and not network and not clipboard)"
+
 
 before_install:
   - echo "before_install"