[fix][python-flask][python-aiohttp]: incorrect boolean literal in unit tests

Created by: Kevin-Bannier

Fixes #9386 (closed)

When using generators python-flaskand python-aiohttp, the generated test body boolean values reads now as follows ("True" or "False"):

body = {
  "boolean_property": True
}

Previous buggy generated code:

body = {
  "boolean_property": true
}

Most of the code is copy-paste from generator python-fastapi(PythonFastAPIServerCodegen.java)

Steps to see the new generated code:

java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate \
   -i modules/openapi-generator/src/test/resources/3_0/petstore.yaml \
   -g python-flask \
   -o /var/tmp/python-flask
cat /var/tmp/python-flask/openapi_server/test/test_store_controller.py

java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate \
   -i modules/openapi-generator/src/test/resources/3_0/petstore.yaml \
   -g python-aiohttp \
   -o /var/tmp/python-aiohttp

cat /var/tmp/python-aiohttp/tests/test_store_controller.py

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