Replace an unnecessary .get().is_some() check

This fixes a warning from the new `unnecessary_get_then_check` Clippy
lint [0] that got added in `1.78.0`.

[0]: https://rust-lang.github.io/rust-clippy/master/index.html#/unnecessary_get_then_check

Signed-off-by: Michael Weiss <[email protected]>

src/config/not_validated.rs

@@ -298,7 +298,7 @@ mod tests {
         assert!(changelog.is_ok());
         let changelog = changelog.unwrap();
         for i in 0..=CONFIGURATION_VERSION {
-            assert!(changelog.get(&i.to_string()).is_some());
+            assert!(changelog.contains_key(&i.to_string()));
         }
     }