refactor: move .python-version file to the root, increase patch version (#144)

Most version managers interpret the `.python-version` file from the root and apply the
python version specified to all child folders.  Moving the `.pythong-version` file
to the root of the project ensures that the python version is the same for all
actions, but most importantly avoids a situation when running `./bin/setup_venv.sh`
from the root where the system python will be hooked for the venv.

Author: 4141done

.python-version

@@ -0,0 +1 @@
+3.9.12

bin/setup_venv.sh

@@ -104,7 +104,7 @@ fi
 if command -v pyenv >/dev/null; then
   eval "$(pyenv init --path)"
   eval "$(pyenv init -)"
-  pyenv install --skip-existing <"${script_dir}/../pulumi/python/.python-version"
+  pyenv install --skip-existing <"${script_dir}/../.python-version"
 
   # If the pyenv-virtualenv tools are installed, prompt the user if they want to
   # use them.