Apply nightly clippy fixes (#11083)

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# Description
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Clippy fixes for rust 1.76.0-nightly

# User-Facing Changes
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helps us keep track of breaking changes. -->

N/A
# Tests + Formatting
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crates/nu-cli/tests/completions.rs

@@ -122,14 +122,14 @@ fn dotnu_completions() {
     let suggestions = completer.complete(&completion_str, completion_str.len());
 
     assert_eq!(1, suggestions.len());
-    assert_eq!("custom_completion.nu", suggestions.get(0).unwrap().value);
+    assert_eq!("custom_completion.nu", suggestions.first().unwrap().value);
 
     // Test use completion
     let completion_str = "use ".to_string();
     let suggestions = completer.complete(&completion_str, completion_str.len());
 
     assert_eq!(1, suggestions.len());
-    assert_eq!("custom_completion.nu", suggestions.get(0).unwrap().value);
+    assert_eq!("custom_completion.nu", suggestions.first().unwrap().value);
 }
 
 #[test]
@@ -141,7 +141,7 @@ fn external_completer_trailing_space() {
 
     let suggestions = run_external_completion(block, &input);
     assert_eq!(3, suggestions.len());
-    assert_eq!("gh", suggestions.get(0).unwrap().value);
+    assert_eq!("gh", suggestions.first().unwrap().value);
     assert_eq!("alias", suggestions.get(1).unwrap().value);
     assert_eq!("", suggestions.get(2).unwrap().value);
 }
@@ -153,7 +153,7 @@ fn external_completer_no_trailing_space() {
 
     let suggestions = run_external_completion(block, &input);
     assert_eq!(2, suggestions.len());
-    assert_eq!("gh", suggestions.get(0).unwrap().value);
+    assert_eq!("gh", suggestions.first().unwrap().value);
     assert_eq!("alias", suggestions.get(1).unwrap().value);
 }
 
@@ -164,7 +164,7 @@ fn external_completer_pass_flags() {
 
     let suggestions = run_external_completion(block, &input);
     assert_eq!(3, suggestions.len());
-    assert_eq!("gh", suggestions.get(0).unwrap().value);
+    assert_eq!("gh", suggestions.first().unwrap().value);
     assert_eq!("api", suggestions.get(1).unwrap().value);
     assert_eq!("--", suggestions.get(2).unwrap().value);
 }