Fix type in test_escape test

On machines where char is unsigned this could lead to option parsing looping
endlessly. It's also too narrow a type on other hardware.

Found via Tom Lane's monitoring of the buildfarm.

Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Security: CVE-2025-1094
Backpatch-through: 13

src/test/modules/test_escape/test_escape.c

@@ -740,7 +740,7 @@ int
 main(int argc, char *argv[])
 {
 	pe_test_config tc = {0};
-	char		c;
+	int			c;
 	int			option_index;
 
 	static const struct option long_options[] = {