[docs] Fix Typo issue from passprase to passphrase

[lamtrinhdev]

• The change/commits follow the Mullvad coding guidelines: https://github.com/mullvad/coding-guidelines
• The PR description should describe:
  Fix Typo issue from passprase to passphrase at docs/macos-signing.md.

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This change is 

[lamtrinhdev]

Dear @faern ,

I have a minor update at docs/macos-signing.md with correct the word. Could you please help me to review it?

Thanks,
Lam

[faern]

Thank you! This looks good.

[lamtrinhdev]

Dear @faern ,

Thank you for your review. I do not have permission to merge. Could you help me to merge the PR?

Thanks,
Lam

[faern]

Thank you for your contribution.