Remove non-existent MUSCL test from CI workflow

Author: Guo-astro

.github/workflows/shamrock-acpp-phys-test.yml

@@ -55,10 +55,6 @@ jobs:
             testfile: gsph/sod_tube_gsph.py
           - worldsize: 2
             testfile: gsph/sod_tube_gsph.py
-          - worldsize: 1
-            testfile: gsph/sod_tube_gsph_muscl.py
-          - worldsize: 2
-            testfile: gsph/sod_tube_gsph_muscl.py
           - worldsize: 1
             testfile: comp_phantom_sedov_1patch.py
           - worldsize: 2