Disable non-cron travis jobs

This was already done for PHP-8.0 and master, do it for PHP-7.4
as well.

Author: nikic

.travis.yml

@@ -70,10 +70,13 @@ jobs:
     include:
         - env: ENABLE_MAINTAINER_ZTS=0 ENABLE_DEBUG=0
           arch: amd64
+          if: type = cron
         - env: ENABLE_MAINTAINER_ZTS=1 ENABLE_DEBUG=1
           arch: amd64
+          if: type = cron
         - env: ENABLE_MAINTAINER_ZTS=1 ENABLE_DEBUG=1 SKIP_IO_CAPTURE_TESTS=1 ARM64=1
           arch: arm64
+          if: type = cron
 
 before_script:
     - ccache --version