[CI] Support python flake8

[shahmishal]

Remove python_lint_check_enabled from CI .github/workflows/pull_request.yml file to re-enable testing.

Run pip3 install flake8 flake8-import-order
  pip3 install flake8 flake8-import-order
  cd ${GITHUB_WORKSPACE}
  if [ ! -f ".flake8" ]; then
    echo "Downloading default flake8 config file"
    curl -s https://raw.githubusercontent.com/swiftlang/github-workflows/refs/heads/main/.github/workflows/configs/.flake8 > .flake8
  fi
  flake8
  shell: /usr/bin/bash -e {0}
Defaulting to user installation because normal site-packages is not writeable
Collecting flake8
  Downloading flake8-7.1.1-py2.py3-none-any.whl (57 kB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 57.7/57.7 KB 3.2 MB/s eta 0:00:00
Collecting flake8-import-order
  Downloading flake8_import_order-0.18.2-py2.py3-none-any.whl (15 kB)
Collecting pyflakes<3.3.0,>=3.2.0
  Downloading pyflakes-3.2.0-py2.py3-none-any.whl (62 kB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 62.7/62.7 KB 12.7 MB/s eta 0:00:00
Collecting pycodestyle<2.13.0,>=2.12.0
  Downloading pycodestyle-2.12.1-py2.py3-none-any.whl (31 kB)
Collecting mccabe<0.8.0,>=0.7.0
  Downloading mccabe-0.7.0-py2.py3-none-any.whl (7.3 kB)
Requirement already satisfied: setuptools in /usr/lib/python3/dist-packages (from flake8-import-order) (59.6.0)
Installing collected packages: pyflakes, pycodestyle, mccabe, flake8-import-order, flake8
Successfully installed flake8-7.1.1 flake8-import-order-0.18.2 mccabe-0.7.0 pycodestyle-2.12.1 pyflakes-3.2.0
Downloading default flake8 config file
./Utils/gyb.py:41:26: E741 ambiguous variable name 'l'
./Utils/gyb.py:64:70: W504 line break after binary operator
./Utils/gyb.py:602:32: W504 line break after binary operator
./Utils/gyb.py:603:66: W504 line break after binary operator
./Utils/gyb.py:647:47: W504 line break after binary operator
./Utils/gyb.py:738:42: E741 ambiguous variable name 'l'
./Utils/gyb_utils.py:14:3: E111 indentation is not a multiple of 4
./Utils/gyb_utils.py:22:1: E305 expected 2 blank lines after class or function definition, found 1
./Utils/gyb_utils.py:23:1: E302 expected 2 blank lines, found 0
./Utils/gyb_utils.py:30:1: W293 blank line contains whitespace
Error: Process completed with exit code 1.