Add support for the `.AppImage` extension #467

Job	Run time
Alpine Linux	2m 33s
FreeBSD-x86_64 with rust stable	50s
Linux-x86_64 with rust stable	1m 51s
Linux-x86_64 (rustls-native-roots) with rust stable	1m 46s
Linux-x86_64 (native-tls) with rust stable	1m 16s
Linux-x86_64 (native-tls-vendored) with rust stable	1m 28s
Linux-aarch64 with rust stable	1m 23s
Linux-arm with rust stable	1m 22s
Linux-i686 with rust stable	53s
Linux-powerpc with rust stable	44s
Linux-powerpc64 with rust stable	55s
Linux-powerpc64le with rust stable	56s
Linux-riscv64 with rust stable	1m 1s
Linux-s390x with rust stable	1m 0s
NetBSD-x86_64 with rust stable	2m 0s
Windows-aarch64 with rust stable	3m 8s
Windows-i686 with rust stable	3m 58s
Windows-x86_64 with rust stable	3m 23s
macOS-x86_64 with rust stable	1m 42s
macOS-aarch64 with rust stable	1m 23s
Linux-x86_64 with rust beta	3m 41s
Linux-x86_64 with rust nightly	3m 23s
	40m 36s

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