test: get tests running on macOS again by leveraging built-in platform detection

[nperez0111]

Changes Overview

The tests were failing to run on a macOS machine because the keyboard shortcut for strike was trying to implement it's own platform detection.
Instead of relying on the existing keyboard shortcut code:

tiptap/packages/core/src/commands/keyboardShortcut.ts

Lines 30 to 34 in b941eea

	if (isiOS() || isMacOS()) {
	meta = true
	} else {
	ctrl = true
	}

The tests that were being run only ever sent the CTRL key instead of using the platform-independent modKey

Implementation Approach

Simplify the keyboard shortcut handler to utilize the built-in Mod which means CMD on macOS and CTRL on Windows

Testing Done

I ran the demo src/Marks/Strike and everything worked as expected.

Verification Steps

Run the tests on macOS host, and on CI. Verify shortcut on your own

Additional Notes

Checklist

• I have renamed my PR according to the naming conventions. (e.g. feat: Implement new feature or chore(deps): Update dependencies)
• My changes do not break the library.
• I have added tests where applicable.
• I have followed the project guidelines.
• I have fixed any lint issues.

Related Issues

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