Fix regtest doc (#2955)

Author: MonkeyCanCode

regtests/README.md

@@ -185,30 +185,10 @@ Other commands are available in the `regtests/t_spark_sql/src` directory.
 ## Python Tests
 
 Python tests are based on `pytest`. They rely on a python Polaris client, which is generated from the openapi spec.
-The client can be generated using two commands:
+The client can be generated using make command:
 
 ```shell
-# generate the management api client
-docker run --rm \
-  -v ${PWD}:/local openapitools/openapi-generator-cli generate \
-  -i /local/spec/polaris-management-service.yml \
-  -g python \
-  -o /local/client/python --additional-properties=packageName=polaris.management --additional-properties=apiNamePrefix=polaris
-
-# generate the iceberg rest client
-docker run --rm \
-  -v ${PWD}:/local openapitools/openapi-generator-cli generate \
-  -i /local/spec/polaris-catalog-service.yaml \
-  -g python \
-  -o /local/client/python --additional-properties=packageName=polaris.catalog --additional-properties=apiNameSuffix="" --additional-properties=apiNamePrefix=Iceberg
-```
-
-Tests rely on Python 3.9 or higher. `pyenv` can be used to install a current version and mapped to the local directory
-by using
-
-```shell
-pyenv install 3.9
-pyenv local 3.9
+make client-regenerate
 ```
 
 Once you've done that, you can run `setup.sh` to generate a python virtual environment (installed at `~/polaris-venv`)