Bump flask from 1.1.2 to 2.3.2 in /docs/examples/fork-process-model/flask-gunicorn (#3291)

Author: dependabot[bot]

docs/examples/fork-process-model/flask-gunicorn/requirements.txt

@@ -1,5 +1,5 @@
 click==7.1.2
-Flask==1.1.2
+Flask==2.3.2
 googleapis-common-protos==1.52.0
 grpcio==1.56.0
 gunicorn==20.0.4