Add tests for syntax error messages that had no test coverage (GH-153192)

"illegal target for annotation" and "cannot use dict unpacking here"
were not tested at all, and "f-string: expecting '!', or ':', or '}'"
was only tested for its t-string variant.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/test/test_fstring.py

@@ -1706,6 +1706,9 @@ def test_invalid_syntax_error_message(self):
         with self.assertRaisesRegex(SyntaxError,
                                     "f-string: expecting '=', or '!', or ':', or '}'"):
             compile("f'{a $ b}'", "?", "exec")
+        with self.assertRaisesRegex(SyntaxError,
+                                    "f-string: expecting '!', or ':', or '}'"):
+            compile("f'{a=b}'", "?", "exec")
 
     def test_with_two_commas_in_format_specifier(self):
         error_msg = re.escape("Cannot specify ',' with ','.")

Lib/test/test_syntax.py

@@ -2238,6 +2238,16 @@
 Traceback (most recent call last):
 SyntaxError: only single target (not list) can be annotated
 
+>>> 1: int
+Traceback (most recent call last):
+SyntaxError: illegal target for annotation
+>>> -x: int = 1
+Traceback (most recent call last):
+SyntaxError: illegal target for annotation
+>>> (x for x in y): int
+Traceback (most recent call last):
+SyntaxError: illegal target for annotation
+
 # 'not' after operators:
 
 >>> 3 + not 3

Lib/test/test_unpack_ex.py

@@ -355,6 +355,20 @@
         ^^^
     SyntaxError: cannot use dict unpacking in a dictionary value
 
+    >>> (**a)
+    Traceback (most recent call last):
+    ...
+    (**a)
+     ^^
+    SyntaxError: cannot use dict unpacking here
+
+    >>> {**a for a in {1: 2}.items(): b}
+    Traceback (most recent call last):
+    ...
+    {**a for a in {1: 2}.items(): b}
+     ^^
+    SyntaxError: cannot use dict unpacking here
+
 
 # Generator expression in function arguments