Fix bug in python version request

Author: mandli

.github/workflows/testing.yml

@@ -44,7 +44,7 @@ jobs:
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v5
       with:
-        python-version: ${{matrix.python-version}}
+        python-version: ${{ matrix.python-version }}
 
     - name: Set up compilers
       uses: fortran-lang/setup-fortran@v1