Fix test_fstring

Author: lysnikolaou

Grammar/python.gram

@@ -1462,8 +1462,10 @@ invalid_replacement_field:
             TOK_GET_MODE(p->tok)->tstring ? 't' : 'f') }
 
 invalid_conversion_character:
-    | '!' &(':' | '}') { RAISE_SYNTAX_ERROR_ON_NEXT_TOKEN("%c-string: missing conversion character") }
-    | '!' !NAME { RAISE_SYNTAX_ERROR_ON_NEXT_TOKEN("%c-string: invalid conversion character") }
+    | '!' &(':' | '}') { RAISE_SYNTAX_ERROR_ON_NEXT_TOKEN("%c-string: missing conversion character",
+        TOK_GET_MODE(p->tok)->tstring ? 't' : 'f') }
+    | '!' !NAME { RAISE_SYNTAX_ERROR_ON_NEXT_TOKEN("%c-string: invalid conversion character",
+        TOK_GET_MODE(p->tok)->tstring ? 't' : 'f') }
 
 invalid_arithmetic:
     | sum ('+'|'-'|'*'|'/'|'%'|'//'|'@') a='not' b=inversion { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "'not' after an operator must be parenthesized") }

Lib/test/test_fstring.py

@@ -1346,7 +1346,6 @@ def test_conversions(self):
         self.assertAllRaise(SyntaxError, "f-string: expecting '}'",
                             ["f'{3!'",
                              "f'{3!s'",
-                             "f'{3!g'",
                              ])
 
         self.assertAllRaise(SyntaxError, 'f-string: missing conversion character',