Fix GH-17687: initializer-string for array of ... warnings

Starting with gcc 15 the warning `-Wunterminated-string-initialization`
is enabled by default. We make now use of the `nonstring` attribute to
silence the warning for the cases where this is intended.

Closes GH-18603.

ext/pdo/pdo_sqlstate.c

@@ -25,7 +25,7 @@
 #include "php_pdo_driver.h"
 
 struct pdo_sqlstate_info {
-	const char state[5];
+	const char state[5] ZEND_NONSTRING;
 	const char *desc;
 };