Add 'virt' and 'group' settings for arm64-graviton2 (pandas-dev#40959)

Author: martin-g

.travis.yml

@@ -36,6 +36,8 @@ matrix:
 
   include:
     - arch: arm64-graviton2
+      virt: lxd
+      group: edge
       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)"