test cases: fix '8 flex' with C23

With C23 (as upcoming GCC 15 will default to), `void yyerror()` is
the same as `void yyerror(void)`, i.e. `yyerror` takes no arguments.

Fix the prototype given we *do* call it with an error string:
```
pgen.p/parser.tab.c: In function ‘yyparse’:
pgen.p/parser.tab.c:1104:7: error: too many arguments to function ‘yyerror’
 1104 |       yyerror (YY_("syntax error"));
      |       ^~~~~~~
../test cases/frameworks/8 flex/parser.y:3:12: note: declared here
    3 | extern int yyerror();
      |            ^~~~~~~
pgen.p/parser.tab.c:1215:3: error: too many arguments to function ‘yyerror’
 1215 |   yyerror (YY_("memory exhausted"));
      |   ^~~~~~~
../test cases/frameworks/8 flex/parser.y:3:12: note: declared here
    3 | extern int yyerror();
      |            ^~~~~~~
```

Bug: https://bugs.gentoo.org/946625

1 files changed, 1 insertions, 1 deletions

diff --git a/test cases/frameworks/8 flex/parser.y b/test cases/frameworks/8 flex/parser.y
index 663f2f3cf..ba8004efd 100644
--- a/test cases/frameworks/8 flex/parser.y
+++ b/test cases/frameworks/8 flex/parser.y
@@ -1,6 +1,6 @@
 %{
 extern int yylex(void);
-extern int yyerror();
+extern int yyerror(char *s);
 %}
 
 %token BOOLEAN