Disable build scans for pull requests being built on s390x

For some reason, the Develocity Gradle Plugin fails to run
./gradlew buildScanPublishPrevious and spits out errors like this:

```
Publishing build scan...

The Gradle Enterprise server (ge.hibernate.org) rejected the request due to authentication being required.
If you are able to sign in to this server in a web browser, you can authenticate your environment by running the following task:

:provisionGradleEnterpriseAccessKey

Or see https://gradle.com/help/gradle-plugin-auth for additional help with authenticating your build environment.

FAILURE: Build failed with an exception.
```

Jenkinsfile

@@ -250,7 +250,7 @@ void ciBuild(buildEnv, String args) {
 			}
 		}
 	}
-	else {
+	else if ( buildEnv.node && buildEnv.node != 's390x' ) { // We couldn't get the code below to work on s390x for some reason.
 		// Pull request: we can't pass credentials to the build, since we'd be exposing secrets to e.g. tests.
 		// We do the build first, then publish the build scan separately.
 		tryFinally({
@@ -264,6 +264,10 @@ void ciBuild(buildEnv, String args) {
 			}
 		})
 	}
+	else {
+		// Don't do build scans
+		sh "./ci/build.sh $args"
+	}
 }
 
 void pruneDockerContainers() {