.gitattributes: add Rust diff and merge attributes

Set rust source code to diff=rust (built-in with new git versions)
and merge=binary for Cargo.lock files (they should not be merged but
auto-generated by cargo)

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Link: https://lore.kernel.org/r/278e3878b40ecc7c424dec1ed978eedf21469f52.1727961605.git.manos.pitsidianakis@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

.gitattributes

@@ -2,3 +2,6 @@
 *.h.inc         diff=c
 *.m             diff=objc
 *.py            diff=python
+*.rs            diff=rust
+*.rs.inc        diff=rust
+Cargo.lock      diff=toml merge=binary