Add workflow_dispatch trigger & specify poetry version

Author: jonasvdd

.github/workflows/deploy-mkdocs.yml

@@ -4,6 +4,7 @@ on:
   push:
     tags:
       - "*"
+  workflow_dispatch: {}
 
 jobs:
   deploy:
@@ -21,6 +22,8 @@ jobs:
 
       - name: Install Poetry
         uses: snok/install-poetry@v1
+        with:
+          version: 1.5.1
 
       - name: Cache Poetry
         id: cached-poetry-dependencies