Update Python versions in "pytest" workflow

- Add Python 3.13
- Drop Python 3.8

.github/workflows/pytest.yaml

@@ -27,19 +27,19 @@ jobs:
         # release. Only test SparseDataArray where possible.
         # Earliest version supported by genno = earliest Python that has not
         # reached EOL
-        - {version: "3.8", extras: ",sparse"}
         - {version: "3.9", extras: ",sparse"}
         - {version: "3.10", extras: ",sparse"}
         - {version: "3.11", extras: ",sparse"}
-        # Latest release / latest supported by genno / testable on GHA
         - {version: "3.12", extras: ",sparse"}
+        # Latest release / latest supported by genno / testable on GHA
+        - {version: "3.13-rc.2", extras: ",sparse"}
 
         # For fresh releases and development versions of Python, compiled binary
         # wheels are not available for some dependencies, e.g. numpy, pandas.
         # Compiling these on the job runner requires a more elaborate build
         # environment, currently out of scope for genno. Exclude these versions
         # from CI.
-        # - {version: "3.13.0-rc.1", extras: ""}  # Development version
+        # - {version: "3.14.0-beta.1", extras: ""}  # Development version
 
       fail-fast: false