ci(dependency-cache): add workflow call output

Ref: #65
Signed-off-by: Philip Gerke <me@philipgerke.com>

Author: pgerke

.github/workflows/dependency_cache.yml

@@ -1,5 +1,9 @@
 on:
-  - workflow_call
+  workflow_call:
+    outputs:
+      pnpm-store-path:
+        description: "The path to the pnpm store"
+        value: ${{ jobs.cache_dependencies.outputs.pnpm-store-path }}
 
 jobs:
   cache_dependencies: