Fix incorrect supported architectures for RustDesk

[StrangeRanger]

NOTES:

• On Debian based distributions, dpkg --print-architecture will never:
  • output aarch64, but instead will use arm64.
  • output armv7, but instead will use armhf
  • 

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PR NOTES:

• For the past year, armv7 releases for deb packages have only ever included armv7-sciter.deb. As it stood, the script would never be able to get and install the deb for the armv7 architecture.
• As mentioned in the above notes, dpkg will never output aarch64 or armv7. As a result, the program would never have been able to install arm based systems.

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FINAL NOTES:

• I have not been able to test the changes directly, so please review them closely to ensure the grep patterns is properly implemented.
• This PR fixes issue 1415

[StrangeRanger]

I have no idea why the test is failing. Maybe because it's trying to save the deb to the deb-get cache?

[StrangeRanger]

https://github.com/wimpysworld/deb-get/pull/1416 might be prefered over this one, since it passes the checks.