Fix typo.

Author: fabiocaccamo

.github/workflows/test-package.yml

@@ -15,7 +15,7 @@ jobs:
       fail-fast: false
       matrix:
         platform: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: ['3.10', '3.11', '3.12', '3.13', pypy-3.10']
+        python-version: ['3.10', '3.11', '3.12', '3.13', 'pypy-3.10']
 
     steps: