Only skip building wheels on PR builds (#10482)

Building on all branch builds has the following benefits:
1) We'll detect the release process breaking before the day of a release.
2) Downstream users can consume any arbitrary Pants commit.

[ci skip-rust]

.travis.yml

@@ -615,7 +615,8 @@ jobs:
     - PANTS_REMOTE_CA_CERTS_PATH=/usr/lib/google-cloud-sdk/lib/third_party/grpc/_cython/_credentials/roots.pem
     - PREPARE_DEPLOY=1
     - CACHE_NAME=wheels.linux
-    if: commit_message !~ /\[ci skip-build-wheels\]/
+    if: commit_message !~ /\[ci skip-build-wheels\]/ OR type NOT IN (pull_request,
+      cron)
     language: python
     name: Build Linux wheels and fs_util
     os: linux
@@ -668,7 +669,8 @@ jobs:
     - BOOTSTRAPPED_PEX_KEY_SUFFIX=py36.osx
     - PREPARE_DEPLOY=1
     - CACHE_NAME=wheels.osx
-    if: commit_message !~ /\[ci skip-build-wheels\]/
+    if: commit_message !~ /\[ci skip-build-wheels\]/ OR type NOT IN (pull_request,
+      cron)
     language: generic
     name: Build macOS wheels and fs_util
     os: osx

build-support/bin/generate_travis_yml.py

@@ -436,7 +436,9 @@ def osx_shard(
 
 # See https://docs.travis-ci.com/user/conditions-v1.
 SKIP_RUST_CONDITION = r"commit_message !~ /\[ci skip-rust\]/"
-SKIP_WHEELS_CONDITION = r"commit_message !~ /\[ci skip-build-wheels\]/"
+SKIP_WHEELS_CONDITION = (
+    r"commit_message !~ /\[ci skip-build-wheels\]/ OR type NOT IN (pull_request, cron)"
+)
 
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 # Bootstrap engine