Replace gettype() with get_debug_type() in exception messages

get_debug_type() does the same thing but better (spelling type names
in the same way as in type declarations, and including names of
object classes and resource types). It was added in PHP 8, but the
symfony/polyfill-php80 package provides it while we still support 7.4.

For reference:
https://www.php.net/manual/en/function.get-debug-type.php
https://www.php.net/manual/en/function.gettype.php

Change-Id: Ib07dccfe476adc203371a9082e52db56cba2e057

SimpleCaptcha/SimpleCaptcha.php

@@ -630,7 +630,7 @@ class SimpleCaptcha {
 		if ( $newtext !== null && $wgCaptchaRegexes ) {
 			if ( !is_array( $wgCaptchaRegexes ) ) {
 				throw new UnexpectedValueException(
-					'$wgCaptchaRegexes is required to be an array, ' . gettype( $wgCaptchaRegexes ) . ' given.'
+					'$wgCaptchaRegexes is required to be an array, ' . get_debug_type( $wgCaptchaRegexes ) . ' given.'
 				);
 			}
 			// Custom regex checks. Reuse $oldtext if set above.