Only use travis for cron jobs

Our primary CI has been Azure Pipelines for a while now already.
Travis was primarily retained as a) a fast feedback builder and
b) to test architectures not available elsewhere.

Due to Travis CI open source policy changes, Travis is no longer
useful as a fast feedback builder. As such, only use it for cron
job builds.

Author: nikic

.travis.yml

@@ -70,8 +70,10 @@ jobs:
     include:
         - env: ENABLE_ZTS=0 ENABLE_DEBUG=0
           arch: amd64
+          if: type = cron
         - env: ENABLE_ZTS=1 ENABLE_DEBUG=1
           arch: amd64
+          if: type = cron
         - env: ENABLE_ZTS=1 ENABLE_DEBUG=1 SKIP_IO_CAPTURE_TESTS=1 ARM64=1
           arch: arm64
           if: type = cron