Spell pypy3.10 consistently

The documentation for setup-python says "pypy3.10-7.x.y" for a specific
pypy3 7.x.y release that supports the Python 3.10 language, so let's
avoid a - between pypy and the python language version, even if it works
today.

.github/workflows/build.yml

@@ -26,7 +26,7 @@ jobs:
           - "3.11"
           - "3.12"
           - "3.13"
-          - "pypy-3.10"
+          - "pypy3.10"
 
     steps:
       - name: Git clone