git: bump zlib-rs to 0.6.4 for loose object fixes

This zlib-rs release fixes bugs that could make zlib output written by
gix's zlib-rs backend unreadable later[1][2]. jj uses that path when
writing loose Git objects, so an affected commit could appear to succeed
even though the object later failed to inflate or failed its zlib checksum.

[1] https://github.com/trifectatechfoundation/zlib-rs/pull/504
[2] https://github.com/trifectatechfoundation/zlib-rs/pull/520

CHANGELOG.md

@@ -54,6 +54,11 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   remote's fetch URL or effective push URL.
   [#413](https://github.com/jj-vcs/jj/issues/413)
 
+* Fixed corrupt loose Git objects written through zlib-rs. Previously, jj could
+  report a successful commit even though `git fsck` later failed with
+  `incorrect data check`, `corrupt loose object`, or `missing blob`, and later
+  jj operations could fail with `corrupt deflate stream`.
+
 ## [0.42.0] - 2026-06-04
 
 ### Release highlights

Cargo.lock

@@ -5569,9 +5569,9 @@ dependencies = [
 
 [[package]]
 name = "zlib-rs"
-version = "0.6.3"
+version = "0.6.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3be3d40e40a133f9c916ee3f9f4fa2d9d63435b5fbe1bfc6d9dae0aa0ada1513"
+checksum = "977347db8caa080403f6b6b7c1cda9479a8e869316f7e13a59b19076a40f94e3"
 
 [[package]]
 name = "zmij"