Check for required inputs.

Author: desrosj

.github/workflows/backport.yml

@@ -45,8 +45,23 @@ on:
 permissions: {}
 
 jobs:
+  validate-inputs:
+    name: Validate inputs
+    runs-on: ubuntu-24.04
+    steps:
+      - name: Ensure a commit SHA or PR numbers are provided
+        env:
+          INPUTS_COMMIT_SHA: ${{ inputs.commit-sha }}
+          INPUTS_PR_NUMBERS: ${{ inputs.pr_numbers }}
+        run: |
+          if [ -z "${INPUTS_COMMIT_SHA}" ] && [ -z "${INPUTS_PR_NUMBERS}" ]; then
+            echo "::error::A commit SHA or PR number(s) must be included."
+            exit 1
+          fi
+
   get-branches:
     name: Get target branches
+    needs: [ 'validate-inputs' ]
     runs-on: ubuntu-24.04
     outputs:
       branches: ${{ steps.branches.outputs.result }}
@@ -82,7 +97,7 @@ jobs:
 
   backport:
     name: 'Backport to ${{ matrix.branch }}'
-    needs: [ 'get-branches' ]
+    needs: [ 'validate-inputs', 'get-branches' ]
     if: ${{ needs.get-branches.outputs.branches != '[]' }}
     runs-on: ubuntu-24.04
     permissions: