Bump git2 from 0.20.2 to 0.20.4

Bumps [git2](https://github.com/rust-lang/git2-rs) from 0.20.2 to 0.20.4.
- [Changelog](https://github.com/rust-lang/git2-rs/blob/git2-0.20.4/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/git2-rs/compare/git2-0.20.2...git2-0.20.4)

---
updated-dependencies:
- dependency-name: git2
  dependency-version: 0.20.4
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

src/tools/miri/Cargo.lock

@@ -562,9 +562,9 @@ checksum = "e629b9b98ef3dd8afe6ca2bd0f89306cec16d43d907889945bc5d6687f2f13c7"
 
 [[package]]
 name = "git2"
-version = "0.20.2"
+version = "0.20.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2deb07a133b1520dc1a5690e9bd08950108873d7ed5de38dcc74d3b5ebffa110"
+checksum = "7b88256088d75a56f8ecfa070513a775dd9107f6530ef14919dac831af9cfe2b"
 dependencies = [
  "bitflags",
  "libc",
@@ -804,9 +804,9 @@ dependencies = [
 
 [[package]]
 name = "libgit2-sys"
-version = "0.18.2+1.9.1"
+version = "0.18.3+1.9.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1c42fe03df2bd3c53a3a9c7317ad91d80c81cd1fb0caec8d7cc4cd2bfa10c222"
+checksum = "c9b3acc4b91781bb0b3386669d325163746af5f6e4f73e6d2d630e09a35f3487"
 dependencies = [
  "cc",
  "libc",