ci: pull request template includes sample format (#1357) (#740)

Source-Link: https://github.com/googleapis/synthtool/commit/e122cb03ea37652946651346736d99b9dcc4311f
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:387835a1375a0049ec44e02542c844302854c732d8291bdf8e472c0ff70a8f67