maker-flatpak: Building for arm64 is broken

[pano9000]

Pre-flight checklist

• I have read the contribution documentation for this project.
• I agree to follow the code of conduct that this project uses.
• I have searched the issue tracker for a bug that matches the one I want to file, without success.

Electron Forge version

7.6.1

Electron version

34.0.2

Operating system

Ubuntu 24.04

Last known working Electron Forge version

No response

Expected behavior

Running

$ npx electron-forge make --arch=arm64

should correctly build an arm64/aarch64 Flatpak

Actual behavior

Currently this will fail

❯ Making distributables
  ✖ Making a flatpak distributable for linux/arm64
    › flatpak failed with status code 1

Bit useless, but the trace is:

Error: flatpak failed with status code 1
at ChildProcess.<anonymous> (/home/pano/Programming/0_repos/TriliumNextNotes/node_modules/@malept/flatpak-bundler/index.js:73:16)
    at ChildProcess.emit (node:events:520:28)
    at ChildProcess.emit (node:domain:488:12)
    at maybeClose (node:internal/child_process:1105:16)
    at ChildProcess._handle.onexit (node:internal/child_process:305:5)

However if I enable the debugging messages, we can see it trying to use "arm64" as platform, which fails, because Flatpak does not use "arm64", but "aarch64" as identifier:

$ flatpak info --show-commit --user org.freedesktop.Platform/arm64/24.08
$ flatpak info --show-commit --system org.freedesktop.Platform/arm64/24.08
$ flatpak install --user --no-deps --arch arm64 --assumeyes runtime/org.freedesktop.Platform/arm64/24.08

if we manually call the last command, it shows why it fails:

$ flatpak install --user --no-deps --arch arm64 --assumeyes runtime/org.freedesktop.Platform/arm64/24.08
Error: No remote refs found for ‘runtime/org.freedesktop.Platform/arm64/24.08’

If we manually call the last command, but exchange arm64 with the correct arch identifier, it succeeds and starts downloading/installing

$ flatpak install --user --no-deps --arch aarch64 --assumeyes runtime/org.freedesktop.Platform/aarch64/24.08

Steps to reproduce

$ npx electron-forge make --arch=arm64

Additional information

Will open up a PR that fixes this in a second and link it back here.
It'll do the same thing, that is currently done for "x64" architecture, where Flatpak actually uses "x86_64" as their arch identifiert