Run CodSpeed workflow on Ubuntu 22.04

Ubuntu 24.04, which recently became the default version for the `ubuntu-latest` label,
doesn't seem to be yet supported by the CodSpeed action:

```
Error: Failed to prepare environment: Error: Only Ubuntu 20.04 and 22.04 are supported for now
```

https://github.com/python-pendulum/pendulum/actions/runs/12788370535/job/35649510157?pr=874

.github/workflows/codspeed.yml

@@ -11,7 +11,7 @@ on:
 
 jobs:
   benchmarks:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v3