Update Github pull request template (#5060)

Add option to advise to run non-mainnet acceptance test if required

Signed-off-by: Usman Saleem <usman@usmans.info>

.github/pull_request_template.md

@@ -12,6 +12,10 @@
 - [ ] I thought about documentation and added the `doc-change-required` label to this PR if
     [updates are required](https://wiki.hyperledger.org/display/BESU/Documentation).
 
+## Acceptance Tests (Non Mainnet)
+
+- [ ] I have considered running `./gradlew acceptanceTestNonMainnet` locally if my PR affects non-mainnet modules.
+
 ## Changelog
 
 - [ ] I thought about the changelog and included a [changelog update if required](https://wiki.hyperledger.org/display/BESU/Changelog).