[PRMP-1567] Use '_' consistently in variable names (missed preprod)

Author: robg-test

.github/workflows/run-bulk-upload-pre-prod.yml

@@ -28,6 +28,6 @@ jobs:
       environment: pre-prod
       sandbox: "pre-prod"
       combi_settings: "${{ inputs.combi_settings }}"
-      file-count: "${{ inputs.file_count }}"
+      file_count: "${{ inputs.file_count }}"
     secrets:
       AWS_ASSUME_ROLE: ${{ secrets.AWS_ASSUME_ROLE }}