[Bug?] Cargo.toml can not be found despite a successful release build

[kevin-wijnen]

Trying to compile a project with a Cargo.toml referring to a specific package seems to fail, as Cargo AppImage can not find the Cargo.toml.

After a successful CI build, it simply gives the generic error of not being able to find the Cargo.toml.

     Running `/home/runner/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/rustc --crate-name ruffle_desktop --edition=2021 desktop/src/main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type bin --emit=dep-info,link -C opt-level=3 -C panic=abort -C embed-bitcode=no --cfg 'feature="default"' --cfg 'feature="ruffle_video_software"' --cfg 'feature="software_video"' -C metadata=ac58b6130656ebf8 -C extra-filename=-ac58b6130656ebf8 --out-dir /home/runner/work/ruffle-appimage/ruffle-appimage/target/release/deps -L dependency=/home/runner/work/ruffle-appimage/ruffle-appimage/target/release/deps --extern anyhow=/home/runner/work/ruffle-appimage/ruffle-appimage/target/release/deps/libanyhow-b41453dd2f9d0be1.rlib --extern arboard=/home/runner/work/ruffle-appimage/ruffle-appimage/target/release/deps/libarboard-450afd28690c6ebc.rlib --extern async_io=/home/runner/work/ruffle-appimage/ruffle-appimage/target/release/deps/libasync_io-e07d8bc91e76394b.rli...
    Finished release [optimized] target(s) in 8m 36s
Error: Cannot load metadata from Cargo.toml
Error: Process completed with exit code 1.```

I have been trying to compile [this project](https://github.com/kevin-wijnen/ruffle-appimage/tree/appimage).