Bump to Python 3.9.4

I can PyCharm debug with this, unlike 3.9.3 :)

.github/workflows/windows-build.yml

@@ -19,7 +19,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
         with:
-          python-version: "3.9.3"
+          python-version: "3.9.4"
           architecture: "x86"
 
       - name: Install python tools

.python-version

@@ -1 +1 @@
-3.9.3
+3.9.4