Change diff-poetry-lock action to v0.0.3

Updated the action used for diffing poetry.lock to a specific commit version for v0.0.3

Author: colindean

.github/workflows/poetry-checks.yml

@@ -26,5 +26,5 @@ jobs:
         persist-credentials: false
     # This will post a comment on PRs when poetry.lock changes
     - name: Diff poetry.lock
-      uses: colindean/diff-poetry-lock@nl
+      uses: target/diff-poetry-lock@1ef13108b924e907ed695ac172503091bd0129d4 # v0.0.3