Quote python-version 3.9.1 in lint workflow

Author: Евгений Блинов

.github/workflows/lint.yml

@@ -13,7 +13,7 @@ jobs:
           - os: ubuntu-latest
             python-version: 3.9
           - os: ubuntu-20.04
-            python-version: 3.9.1
+            python-version: "3.9.1"
           - os: ubuntu-latest
             python-version: 3.10
           - os: ubuntu-latest