Adding dependabot file to update GH action versions (#1681)

Author: antonwolfy

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"

.github/workflows/build-sphinx.yml

@@ -193,6 +193,8 @@ jobs:
     permissions:
       # Needed to remove docs for closed pull request from the repo
       contents: write
+      # Needed to modify a comment in the pull request's issue
+      pull-requests: write
 
     runs-on: ubuntu-20.04