Try with subaction

.gitattributes

@@ -0,0 +1 @@
+* text eol=lf

.github/PHPUnitSettings.php

@@ -0,0 +1,3 @@
+<?php
+
+wfLoadExtension( 'examples' );

.github/workflows/main.yml

@@ -15,4 +15,9 @@ jobs:
           php: 7.4
           mwbranch: REL1_39
           extension: DummyExtension
-
+          dependencies:
+            - name: examples
+              checkout:
+                path: mediawiki/extensions/examples
+                repository: wikimedia/mediawiki-extensions-examples
+          extra_file: .github/PHPUnitSettings.php

action.yml

@@ -26,6 +26,10 @@ inputs:
     description: Use MySQL instead of SQLite
     required: false
     default: false
+  dependencies:
+    description: JSON encoded array of dependencies to pass to checkouts
+    required: false
+    default: '[]'
 runs:
   using: 'composite'
   steps:
@@ -60,6 +64,11 @@ runs:
       with:
         path: mediawiki/${{ inputs.type }}s/${{ inputs.extension }}
 
+    - name: Install dependencies
+      uses: ./dependency-action.yml
+      with:
+        dependencies: ${{ inputs.dependencies }}
+
     - name: Composer updates
       working-directory: mediawiki
       run: composer update

dependency-action.yml

@@ -0,0 +1,22 @@
+name: 'Mediawiki Extension PHPUnit Runner - dependency installer'
+description: 'Installs multiple dependencies at once for the main action'
+author: 'WikiTeq'
+branding:
+  color: yellow
+  icon: book
+inputs:
+  dependencies:
+    description: JSON encoded array of dependencies to pass to checkouts
+    required: false
+    default: '[]'
+runs:
+  using: 'composite'
+  strategy:
+    matrix:
+      deps: ${{ fromJson( inputs.dependencies ) }}
+  steps:
+    - uses: actions/checkout@v4
+      with:
+        path: ${{ matrix.deps.path }}
+        repository: ${{ matrix.deps.repository }}
+        token: ${{ matrix.deps.token || '' }}