rust: update to use libgit2 1.9

[chenrui333]

• Have you followed the guidelines for contributing?
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• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
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---

• Update libgit2 to 1.9 rust-lang/cargo#15018

[chenrui333]

Building tool cargo (stage2 -> stage3, aarch64-apple-darwin)
  error: failed to select a version for the requirement `git2 = "^0.20.0"` (locked to 0.20.0)
  candidate versions found which didn't match: 0.19.0, 0.13.25
  location searched: directory source `/private/tmp/rust-20250108-7965-9linw2/rustc-1.83.0-src/vendor` (which is replacing registry `crates-io`)
  required by package `cargo-test-support v0.5.0 (/private/tmp/rust-20250108-7965-9linw2/rustc-1.83.0-src/src/tools/cargo/crates/cargo-test-support)`
  perhaps a crate was updated and forgotten to be re-vendored?
  Build completed unsuccessfully in 0:11:47
  make: *** [all] Error 1

[chenrui333]

seems a bit tricky to patch, let's revisit in next rust release.

[chenrui333]

seems a bit tricky to patch, let's revisit in next rust release.

#203747