rust: docs: add missing newline to printing macro examples

Fix adding a newline at the end of the usage of pr_info! in the
documentation

Fixes: e3c3d34 ("docs: rust: Add description of Rust documentation test as KUnit ones")
Reported-by: Miguel Ojeda <ojeda@kernel.org>
Link: Rust-for-Linux#1139
Signed-off-by: Alban Kurti <kurti@invicto.ai>
Reviewed-by: David Gow <davidgow@google.com>
Link: https://lore.kernel.org/r/20250206-printing_fix-v3-1-a85273b501ae@invicto.ai
[ Replaced Closes with Link since it fixes part of the issue. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: albankurti

Documentation/rust/testing.rst

@@ -97,7 +97,7 @@ operator are also supported as usual, e.g.:
 
 	/// ```
 	/// # use kernel::{spawn_work_item, workqueue};
-	/// spawn_work_item!(workqueue::system(), || pr_info!("x"))?;
+	/// spawn_work_item!(workqueue::system(), || pr_info!("x\n"))?;
 	/// # Ok::<(), Error>(())
 	/// ```