CI: lint is failing because of output to stderr

[andyfaff]

The lint on CI is currently failing because a pip install step is designed to fail if anything writes to stderr.

  - script: >-
      python -m pip install
      pycodestyle==2.5.0
      pyflakes==2.1.1
    displayName: 'Install tools'
    failOnStderr: true

However, pip is emitting a "You are using pip version 20.2.4; however, version 20.3 is available", which this step treats as an error.
I think we should remove the failOnStderr line.

@tylerjereddy

[tylerjereddy]

Fixed by gh-13181

[andyfaff]

Sorry, just figured it was an easy fix. Closed in #13181.
If the pip install does fail, then the next part of the run will fail because pycodestyle won't be installed.