fix: update hardcoded libgit2 version strings in tests to 1.9.2

The Nix environment provides libgit2 1.9.2 via nixpkgs, which
libgit2-sys picks up at build time instead of using its bundled version.
This caused test assertions that hardcode the libgit2 version string
(appended by libgit2 to patch output) to fail after commit 319bb7f
added new Cargo dependencies, though the exact mechanism by which those
dependencies triggered the switch from the bundled 1.9.1 to the system
1.9.2 remains unclear.

Also bump git2 from 0.20.2 to 0.20.4 in both Cargo.toml files so the
bundled libgit2-sys version (0.18.3+1.9.2) properly aligns with the
1.9.2 version in use.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/lib/mbox_parser.rs b/src/lib/mbox_parser.rs
index 48190ba..f3815f9 100644
--- a/src/lib/mbox_parser.rs
+++ b/src/lib/mbox_parser.rs
@@ -333,7 +333,7 @@ index 0000000..a66525d
 +some content1
 \\ No newline at end of file
 --
-libgit2 1.9.1
+libgit2 1.9.2
 
 "
         .to_string()
@@ -531,7 +531,7 @@ Subject: [PATCH] test
 
 This is the body.
 -- 
-libgit2 1.9.1
+libgit2 1.9.2
 
 diff --git a/file.txt b/file.txt
 ";