manual_inspect: fix clippy::version from 1.78.0 to 1.81.0

Although `manual_inspect`'s PR started some months ago, the lint is only
available in the current nightly (1.81.0), rather than 1.78.0.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

clippy_lints/src/methods/mod.rs

@@ -4121,7 +4121,7 @@ declare_clippy_lint! {
     /// ```no_run
     /// let x = Some(0).inspect(|x| println!("{x}"));
     /// ```
-    #[clippy::version = "1.78.0"]
+    #[clippy::version = "1.81.0"]
     pub MANUAL_INSPECT,
     complexity,
     "use of `map` returning the original item"