Add relative sha comparison

There is no prior sha in the github event context of the workflow. Using relative SHA notation is not perfect, but functional. It is likely to not be sufficient for multiple updates on one day.

Author: chartgerink

.github/workflows/add-doi.yaml

@@ -16,11 +16,6 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v2
 
-      - name: Dump GitHub context
-        env:
-          GITHUB_CONTEXT: ${{ toJson(github.event) }}
-        run: echo "$GITHUB_CONTEXT"
-
       - name: Get changed files
         id: changed-files
         uses: actions/github-script@v6
@@ -31,7 +26,7 @@ jobs:
               {
                 owner: context.repo.owner,
                 repo: context.repo.repo,
-                base: context.payload.before,
+                base: `${context.sha}~1`,
                 head: context.sha,
               },
               (response) => response.data.files