PR: Add macOS-arm64 target platform using M1 runner (Installers)

[mrclary]

Description of Changes

Added macOS-arm64 target platform using M1 runner in response to this blog post.

[pep8speaks]

Hello @mrclary! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file installers-conda/build_installers.py:

Line 269:80: E501 line too long (80 > 79 characters)
Line 300:80: E501 line too long (80 > 79 characters)
Line 331:80: E501 line too long (84 > 79 characters)

• In the file spyder/utils/environ.py:

Line 56:80: E501 line too long (86 > 79 characters)

[ccordoba12]

Thanks @mrclary!