Upgrade to Python 3.9 (#11763)

* Dockerfile to 3.9

* Python version

* More python updates

* 3.9 on GitHub actions and lint updates

* Test out 3.9.11 on GitHub actions

* install python with an action

* formatting: newline

* Also has python code

* only check first level for changed modules
Previous example (source-google-search-console/credentials)

* Test failure: there is no logger.trace

.python-version

@@ -1 +1 @@
-3.7.9
+3.9.11