Fix CI: use absolute path for test case file

The mfc wrapper creates its own tmpdir, so relative paths don't work.
Use absolute path to case.py so it can be found after mfc changes directories.

Author: sbryngelson

.github/workflows/homebrew.yml

@@ -147,11 +147,11 @@ jobs:
       - name: Run MFC test case
         run: |
           echo "Running a simple test case (1D Sod shock tube)..."
-          cd $(mktemp -d)
-          cp $(brew --prefix mfc)/examples/1D_sodshocktube/case.py .
+          TESTDIR=$(mktemp -d)
+          cp $(brew --prefix mfc)/examples/1D_sodshocktube/case.py "$TESTDIR/"
           
           echo "Running with $(sysctl -n hw.ncpu) processors..."
-          mfc run case.py -j $(sysctl -n hw.ncpu)
+          mfc run "$TESTDIR/case.py" -j $(sysctl -n hw.ncpu)
           
           echo "Test case completed successfully!"