cargo-llvm-cov: fix tests (and thus the build)

# If the tests are broken, it's probably for one of two reasons:

#

# 1. The version of llvm used doesn't match the expectations of rustc and/or

#    cargo-llvm-cov. This is relatively unlikely because we pull llvm out of

#    rustc's attrset, so it *should* be the right version as long as this is the

#    case.

#    cargo-llvm-cov.

# 2. Nixpkgs has changed its rust infrastructure in a way that causes

#    cargo-llvm-cov to misbehave under test. It's likely that even though the

#    tests are failing, cargo-llvm-cov will still function properly in actual

, fetchurl

, fetchFromGitHub

, rustPlatform

, rustc

, llvmPackages_19

, git

}:

  owner = "taiki-e";

  homepage = "https://github.com/${owner}/${pname}";

  llvm = rustc.llvmPackages.llvm;

  inherit (llvmPackages_19) llvm;

  # Download `Cargo.lock` from crates.io so we don't clutter up Nixpkgs

  cargoLock = fetchurl {