Add workflow for external pr [skip ci]

.github/workflows/build.yml

@@ -0,0 +1,32 @@
+name: Build external pull request
+on:
+  pull_request:
+    branches:
+      - master
+jobs:
+  maven-verify:
+    if: github.repository_owner != 'entur'
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Copy maven settings
+        run: |
+          wget https://raw.githubusercontent.com/entur/ror-maven-settings/master/.m2/settings.xml -O .github/workflows/settings.xml
+      - uses: actions/setup-java@v4
+        with:
+          java-version: 17.0.13
+          distribution: liberica
+      - name: Cache Maven dependencies
+        uses: actions/cache@v4
+        with:
+          path: ~/.m2/repository
+          key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
+          restore-keys: |
+            ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
+            ${{ runner.os }}-maven-
+            ${{ runner.os }}-
+      - name: Run maven build
+        run: mvn verify -s .github/workflows/settings.xml
+