use different python version for both future jobs

Author: jorisvandenbossche

.github/workflows/unit-tests.yml

@@ -59,7 +59,7 @@ jobs:
             # It will be temporarily activated during tests with locale.setlocale
             extra_loc: "zh_CN"
           - name: "Future infer strings"
-            env_file: actions-311.yaml
+            env_file: actions-312.yaml
             pandas_future_infer_string: "1"
           - name: "Future infer strings (without pyarrow)"
             env_file: actions-311.yaml