Add dedicated error for specifiers with incorrect .* suffix

This should make it clearer how and why this is not valid, thus
providing relevant context to readers.

src/packaging/_parser.py

@@ -225,7 +225,14 @@ def _parse_version_many(tokenizer: Tokenizer) -> str:
     """
     parsed_specifiers = ""
     while tokenizer.check("SPECIFIER"):
+        span_start = tokenizer.position
         parsed_specifiers += tokenizer.read().text
+        if tokenizer.check("VERSION_PREFIX_TRAIL", peek=True):
+            tokenizer.raise_syntax_error(
+                ".* suffix can only be used with `==` or `!=` operators",
+                span_start=span_start,
+                span_end=tokenizer.position + 1,
+            )
         tokenizer.consume("WS")
         if not tokenizer.check("COMMA"):
             break

src/packaging/_tokenizer.py

@@ -78,6 +78,7 @@ def __str__(self) -> str:
     "AT": r"\@",
     "URL": r"[^ \t]+",
     "IDENTIFIER": r"\b[a-zA-Z0-9][a-zA-Z0-9._-]*\b",
+    "VERSION_PREFIX_TRAIL": r"\.\*",
     "WS": r"[ \t]+",
     "END": r"$",
 }

tests/test_requirements.py

@@ -285,6 +285,22 @@ def test_error_when_parens_not_closed_correctly(self) -> None:
             "         ~~~~~~~^"
         )
 
+    def test_error_when_prefix_match_is_used_incorrectly(self) -> None:
+        # GIVEN
+        to_parse = "black (>=20.*) ; extra == 'format'"
+
+        # WHEN
+        with pytest.raises(InvalidRequirement) as ctx:
+            Requirement(to_parse)
+
+        # THEN
+        assert ctx.exconly() == (
+            "packaging.requirements.InvalidRequirement: "
+            ".* suffix can only be used with `==` or `!=` operators\n"
+            "    black (>=20.*) ; extra == 'format'\n"
+            "           ~~~~~^"
+        )
+
     def test_error_when_bracket_not_closed_correctly(self) -> None:
         # GIVEN
         to_parse = "name[bar, baz >= 1.0"