Add test for empty FStringMiddle tok in lambda expr

crates/ruff_python_parser/src/lexer.rs

@@ -2022,6 +2022,16 @@ allowed {x}"""} string""#;
         assert_debug_snapshot!(lex_source(source));
     }
 
+    #[test]
+    fn test_fstring_with_lambda_expression() {
+        let source = r#"
+f"{lambda x:{x}}"
+f"{(lambda x:{x})}"
+"#
+        .trim();
+        assert_debug_snapshot!(lex_source(source));
+    }
+
     fn lex_fstring_error(source: &str) -> FStringErrorType {
         match lex(source, Mode::Module).find_map(std::result::Result::err) {
             Some(err) => match err.error {

crates/ruff_python_parser/src/snapshots/ruff_python_parser__lexer__tests__fstring_with_lambda_expression.snap

@@ -0,0 +1,42 @@
+---
+source: crates/ruff_python_parser/src/lexer.rs
+expression: lex_source(source)
+---
+[
+    FStringStart,
+    Lbrace,
+    Lambda,
+    Name {
+        name: "x",
+    },
+    Colon,
+    Lbrace,
+    Name {
+        name: "x",
+    },
+    Rbrace,
+    FStringMiddle {
+        value: "",
+        is_raw: false,
+    },
+    Rbrace,
+    FStringEnd,
+    Newline,
+    FStringStart,
+    Lbrace,
+    Lpar,
+    Lambda,
+    Name {
+        name: "x",
+    },
+    Colon,
+    Lbrace,
+    Name {
+        name: "x",
+    },
+    Rbrace,
+    Rpar,
+    Rbrace,
+    FStringEnd,
+    Newline,
+]