switch to testing GROMACS 2023.1 for all Python

Only use other GROMACS versions for spot testing at highest supported Python.
Note that we had spurious failures of GROMACS 2021.1 with macOS Python 3.11 in
the XFAIL TestAmber03star.test_mdrun and XFAIL TestAmber03w.test_mdrun.
;

.github/workflows/ci.yaml

@@ -27,7 +27,7 @@ jobs:
       matrix:
         os: [ubuntu-latest, macOS-latest]
         python-version: ["3.8", "3.9", "3.10", "3.11"]
-        gromacs-version: ["2021.1"]
+        gromacs-version: ["2023.1"]
         # Test other GROMACS versions selectively on a recent Python.
         # On macOS only test one GROMACS version and two Python versions
         # to keep the testing matrix manageable.
@@ -53,10 +53,10 @@ jobs:
             gromacs-version: "2020.6"
           - os: ubuntu-latest
             python-version: "3.11"
-            gromacs-version: "2022.4"
+            gromacs-version: "2021.1"       
           - os: ubuntu-latest
             python-version: "3.11"
-            gromacs-version: "2023.1"
+            gromacs-version: "2022.4"
 
 
     env: