Add support for aarch64

[julianfairfax]

Closes #167

I have tested this PR on an am64 and an arm64 device. On both devices, the Flatpak installs and works as intended.

[flathubbot]

Started test build 61119

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Build 61119 failed

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Started test build 61121

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Build 61121 failed

[flathubbot]

Started test build 61123

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Build 61123 failed

[flathubbot]

Started test build 61125

[flathubbot]

Build 61125 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/43762/im.riot.Riot.flatpakref

[flathubbot]

Started test build 61133

[flathubbot]

Build 61133 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/43770/im.riot.Riot.flatpakref

[SISheogorath]

Sorry for the lack of feedback so far. I have to say, I'm not too fond of the idea that we switch back to unpacking .deb packages, now that we finally got the upstream binary builds integrated.

Maybe we can convince upstream to also provide arm64 binaries?

[julianfairfax]

bot, build im.riot.Riot

[flathubbot]

Queued test build for im.riot.Riot.

[julianfairfax]

Maybe we can convince upstream to also provide arm64 binaries?

I opened an issue to request that.

[flathubbot]

Started test build 61977

[flathubbot]

Build 61977 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/44610/im.riot.Riot.flatpakref