ci: Unaccompanied double-quote

Author: JDBetteridge

.github/workflows/pytest-core-mpi.yaml

@@ -119,7 +119,7 @@ jobs:
             --cov \
             --cov-config=.coveragerc \
             --cov-report=xml \
-            tests/test_mpi.py"
+            tests/test_mpi.py
 
     - name: Test acoustic and TTI examples with MPI
       uses: ./.github/actions/docker-run