refactor: update pip if extern managed and global.break-system-packages is true

[SteveLauC]

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Closes #631

From the information provided in #631, even though a pip3 is externally managed, we should still update it if global.break-system-packages is set to true.

[SteveLauC]

Here is a build for x86_64/Linux/musl, @ErnestDong you can give it a test.

[ErnestDong]

It works. Thank you. Happy new year