ci: do not hardcode branch into prism script

Author: the-chris-mitchell

.github/workflows/build-lint-test.yml

@@ -33,7 +33,7 @@ jobs:
               run: npm install -g @stoplight/prism-cli
 
             - name: Start PRISM Server
-              run: ./start-prism.sh feature/prism-changes-mt-v2 & sleep 15
+              run: ./start-prism.sh & sleep 15
               working-directory: Xero-Java/src/test/java/com/xero/api/util
 
             - name: Build and test post generation