Fix print picking tox env on CI (#166)

Author: mondeja

.github/workflows/check.yml

@@ -40,7 +40,7 @@ jobs:
         run: |
           import codecs; import os; import sys
           env = f"TOXENV=py3{sys.version_info[1]}\n"
-          print("Picked:\n{env}for{sys.version}")
+          print(f"Picked:\n{env}for{sys.version}")
           with codecs.open(os.environ["GITHUB_ENV"], "a", "utf-8") as file_handler:
                file_handler.write(env)
         shell: python