Update CI to allow builds on Pull Requests

Author: gerph

.github/workflows/ci.yml

@@ -7,13 +7,14 @@ name: PRM-in-XML
 # Controls when the action will run. Triggers the workflow on:
 #   * push on any branch.
 #   * tag creation for tags beginning with a 'v'
+#   * pull requests
 on:
   push:
     branches: ["*"]
     tags: ["v*"]
-  # Pull request events happen on pull request state transitions, so we probably don't want this here.
-  #pull_request:
-  #  branches: ["*"]
+  pull_request:
+    types: [opened, reopened, synchronize]
+    branches: ["*"]
 
 jobs:
   test-examples:
@@ -71,6 +72,9 @@ jobs:
   test-riscos:
     # The type of runner that the job will run on
     runs-on: ubuntu-24.04
+    timeout-minutes: 20
+    concurrency:
+      group: riscos-build-server
     needs: test-examples #  always run after the baseline tests
 
     # Steps represent a sequence of tasks that will be executed as part of the job
@@ -129,6 +133,9 @@ jobs:
   export-riscos:
     # The type of runner that the job will run on
     runs-on: ubuntu-24.04
+    timeout-minutes: 20
+    concurrency:
+      group: riscos-build-server
     needs: ["test-riscos", "test-platforms"]
 
     outputs: