def: make various punctuation misuses into errors (#7624)

Closes https://github.com/nushell/nushell/issues/7604

src/tests/test_engine.rs

@@ -316,7 +316,10 @@ fn default_value11() -> TestResult {
 
 #[test]
 fn default_value12() -> TestResult {
-    fail_test(r#"def foo [--x:int = "a"] { $x }"#, "default value not int")
+    fail_test(
+        r#"def foo [--x:int = "a"] { $x }"#,
+        "default value should be int",
+    )
 }
 
 #[test]