add missing MIME type to AppImage package

[Mrlinkwii]

it should close #416 in terms of appimages

Description

-adds missing MIME type to the electron builder , x-scheme-handler/x-github-desktop-dev-auth which is mentioned in the red-hat builder and debian builder but not the electron builder

desktop/script/package-debian.ts

Lines 67 to 74 in e2e0483

	mimeType: [
	'x-scheme-handler/x-github-client',
	'x-scheme-handler/x-github-desktop-auth',
	// workaround for handling OAuth flow until we figure out what we're doing
	// with the development OAuth details
	//
	// see https://github.com/shiftkey/desktop/issues/72 for more details
	'x-scheme-handler/x-github-desktop-dev-auth',

desktop/script/package-redhat.ts

Lines 65 to 71 in e2e0483

	'x-scheme-handler/x-github-client',
	'x-scheme-handler/x-github-desktop-auth',
	// workaround for handling OAuth flow until we figure out what we're doing
	// with the development OAuth details
	//
	// see https://github.com/shiftkey/desktop/issues/72 for more details
	'x-scheme-handler/x-github-desktop-dev-auth',

what made me look at this was #416 (comment)

Screenshots

N/A

Release notes

Notes:no-notes

[shiftkey]

Thanks for finding this @Mrlinkwii - I'd forgotten to check here when I applied this to the DEB and RPM installers at the time!

I'm going to merge this and cut a new release tomorrow so we can confirm this is resolved...