Use mpl39 on old pytest test

Author: dstansby

.github/workflows/test_and_publish.yml

@@ -44,7 +44,7 @@ jobs:
         - linux: py312-test-mpl310
         # Test different versions of pytest
         - linux: py312-test-mpldev-pytestdev
-        - linux: py39-test-mpl310-pytest62
+        - linux: py39-test-mpl39-pytest62
         - linux: py39-test-mpl37-pytest54
       coverage: "codecov"