chore: [autoapprove] Pin flake8 version (#1842)

* Update noxfile.py.j2

Pinned flake8 to the latest version (as of Aug2023) to avoid unexpected lint error after version update.

* Update .pre-commit-config.yaml

Author: yinghsienwu

synthtool/gcp/templates/python_library/.pre-commit-config.yaml

@@ -26,6 +26,6 @@ repos:
     hooks:
     - id: black
 -   repo: https://github.com/pycqa/flake8
-    rev: 3.9.2
+    rev: 6.1.0
     hooks:
     - id: flake8

synthtool/gcp/templates/python_library/noxfile.py.j2

@@ -25,6 +25,7 @@ import warnings
 
 import nox
 
+FLAKE8_VERSION = "flake8==6.1.0"
 BLACK_VERSION = "black==22.3.0"
 ISORT_VERSION = "isort==5.10.1"
 LINT_PATHS = ["docs", "google", "tests", "noxfile.py", "setup.py"]
@@ -149,7 +150,7 @@ def lint(session):
     Returns a failure if the linters find linting errors or sufficiently
     serious code quality issues.
     """
-    session.install("flake8", BLACK_VERSION)
+    session.install(FLAKE8_VERSION, BLACK_VERSION)
     session.run(
         "black",
         "--check",