build: Make borrowing compliant with older Rust

src/data.rs

@@ -112,7 +112,7 @@ fn list_layout_sources(
     keyboards_path: Option<PathBuf>,
 ) -> Vec<DataSource> {
     let mut ret = Vec::new();
-
+    {
         let mut add_by_name = |name: &str| {
             if let Some(path) = keyboards_path.clone() {
                 ret.push(DataSource::File(
@@ -136,7 +136,7 @@ fn list_layout_sources(
         };
 
         add_by_name(FALLBACK_LAYOUT_NAME);
-
+    }
     ret
 }