fix: Updated get-pip.py for Python3.6

[CoshUS]

Which issue(s) does this change fix?

N/A

Why is this change necessary?

Our CI is broken due to trying to install pip for Python 3.6 which reached its EOL.

If ($env:INSTALL_PY_36_PIP) {python3.6 get-pip.py --user}
ERROR: This script does not work on Python 3.6 The minimum supported Python version is 3.7. Please use https://bootstrap.pypa.io/pip/3.6/get-pip.py instead.

How does it address the issue?

Download a separate 3.6 script and install it instead.

What side effects does this change have?

N/A

Checklist

• Add input/output type hints to new functions/methods
• Write design document (Do I need to write a design document?)
• Write unit tests
• Write/update functional tests
• Write/update integration tests
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.