Packaging through WhiteBeam installer produces incorrect hash file

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The resulting .SHA256 file produced by cargo run package contains a relative path to the WhiteBeam package, which will produce an error when run through sha256sum -c (or equivalent command).

Erroneous output:

$ cat WhiteBeam_0.2.6_aarch64.SHA256
e192e16265df05403a7aaa544234f74bf7f1957ada5ac7042b06ff1bbe78ddb6  ./target/release/WhiteBeam_0.2.6_aarch64.tar.gz

Expected output:

$ cat WhiteBeam_0.2.6_aarch64.SHA256
e192e16265df05403a7aaa544234f74bf7f1957ada5ac7042b06ff1bbe78ddb6  WhiteBeam_0.2.6_aarch64.tar.gz

Needed for reproducible builds.

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Relevant lines: https://github.com/WhiteBeamSec/WhiteBeam/blob/93d956c68fdc711c7813e58a28d68171d45bcfcf/src/installer/platforms/linux/mod.rs#L171-L172