pid: add Rust files to MAINTAINERS

This files is maintained by Christian Brauner, thus add it to the
relevant MAINTAINERS entry.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/20250714124637.1905722-2-aliceryhl@google.com
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Darksonn

MAINTAINERS

@@ -19834,6 +19834,7 @@ M:	Christian Brauner <christian@brauner.io>
 L:	linux-kernel@vger.kernel.org
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git
+F:	rust/kernel/pid_namespace.rs
 F:	samples/pidfd/
 F:	tools/testing/selftests/clone3/
 F:	tools/testing/selftests/pid_namespace/