Currently when one runs `cargo build` twice without changing anything,
zed lib and binary are gonna get rebuilt every time. I checked out cargo
logs and it turns out we were querying wrong path to `.git/logs/HEAD` in
our build.rs, causing it to rerun on every build and thus marking zed
lib as dirty.
See logs (`CARGO_LOG=cargo::core::compiler::fingerprint=trace cargo
build`):
```
0.501173792s INFO cargo::core::compiler::fingerprint: fingerprint dirty for zed v0.120.0 (/Users/hiro/Projects/zed/crates/zed)/RunCustomBuild/TargetInner { ..: custom_build_target("build-script-build", "/Users/hiro/Projects/zed/crates/zed/build.rs", Edition2021) }
0.501180417s INFO cargo::core::compiler::fingerprint: dirty: FsStatusOutdated(StaleItem(MissingFile("/Users/hiro/Projects/zed/crates/zed/.git/logs/HEAD")))
```
The path to .git directory is relative to crates/zed and not to the
workspace's root.
/cc @maxbrunsfeld
Release Notes:
- N/A
dd730549df