Fix up context variable use

Author: znichollscr

.github/workflows/check-cmor-cvs-table.yaml

@@ -19,8 +19,8 @@ jobs:
 
       - name: Update environment file
         env:
-          CMIP7_CVS_FORK: ${{ github.event.inputs.cmip7-cvs-fork }}
-          CMIP7_CVS_BRANCH: ${{ github.event.inputs.cmip7-cvs-branch }}
+          CMIP7_CVS_FORK: ${{ github.event.pull_request.head.repo.owner.login }}
+          CMIP7_CVS_BRANCH: ${{ github.head_ref || github.ref_name }}
         run: |
           # Update the CMIP7 CVs fork and branch in the environment file
           sed -i -e 's/CMIP7_CVS_FORK=.*/CMIP7_CVS_FORK='"${CMIP7_CVS_FORK}"'/g' cmor-cvs-creation.env