fix(ci/nbviewer): continue on error

see jitterbit/get-changed-files#11 for context

when commits are pushed, then later squashed and re-pushed, the action can fail

workaround is to continue on error, since the list of files changed is still correct

.github/workflows/nbviewer.yml

@@ -20,6 +20,7 @@ jobs:
       - name: get files
         id: files
         uses: jitterbit/get-changed-files@v1
+        continue-on-error: true
 
       - name: add comments
         uses: actions/github-script@v3