.travis: Run race detection builds on master commits only

We had to temporarily subscribe to Travis CI because we consumed our
10000 free credits. Our current plan however only allows for two
concurrent builds. With four builds per commit, we are constantly
running behind, with Travis CI builds now taking longer to be scheduled
than it takes our Jenkins tests to finish. Long gone are the days when
we considered Travis CI a viable smoke test...

This commit attempts to alleviate the issue by running our race
detection builds only on master commits.

Signed-off-by: Paul Chaignon <paul@cilium.io>

.travis.yml

@@ -13,12 +13,14 @@ jobs:
       group: edge
     - arch: amd64
       name: "amd64-race"
+      if: type != pull_request
       env:
         - RACE=1
         - BASE_IMAGE=quay.io/cilium/cilium-runtime:2020-11-16@sha256:e0a7d9cc628f93f086434d633d2ac825b9d0c2fb4c2dd6d8d926b05e85515822
         - LOCKDEBUG=1
     - arch: arm64-graviton2
       name: "arm64-graviton2-race"
+      if: type != pull_request
       env:
         - RACE=1
         - BASE_IMAGE=quay.io/cilium/cilium-runtime:2020-11-16@sha256:e0a7d9cc628f93f086434d633d2ac825b9d0c2fb4c2dd6d8d926b05e85515822