Improve macOS CI workflow: Split build/test and fix naming

[coderabbitai]

Follow-up improvements for macOS CI workflow

This issue tracks improvements suggested during review of PR #5011.

1. Split installer build and testing

Suggestion by @cfergeau:
The installer build and the installer tests on Apple Silicon/Intel should be separate:

• Build one universal installer on Apple Silicon
• Test the installer on both Intel and Apple Silicon platforms
• This is closer to how the installer will be released

Additionally, running crc setup downloads the bundle which can take significant time and may not be ideal for CI.

Reference: #5011 (comment)

2. Normalize naming convention

Suggestion by @cfergeau:
Change "macOS" to "macos" for consistency in the workflow file.

Reference: #5011 (comment)

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Requested by: @anjannath
Related PR: #5011