Cargo.toml: bump Rust version

[oech3]

Since this project is WIP and none of (lts) distribution package it, there is no reason to restrict toolchain at here and build time.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.16%. Comparing base (08d3454) to head (95a2213).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #369   +/-   ##
=======================================
  Coverage   82.16%   82.16%           
=======================================
  Files          13       13           
  Lines        5444     5444           
  Branches      304      304           
=======================================
  Hits         4473     4473           
  Misses        969      969           
  Partials        2        2           

Flag	Coverage Δ
macos_latest	82.61% <ø> (ø)
ubuntu_latest	82.72% <ø> (ø)
windows_latest	0.00% <ø> (ø)

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[xtqqczze]

This crate (unlike uutils/tar#259) has already been released to crates.io, so we should be a little more cautious about MSRV.

It’s also worth noting that, unlike a rust-toolchain file, the rust-version field does not restrict the use of a newer toolchain.