Site Health: Do not trigger the fatal error handler while updates are being installed.

Triggering the error handler during updates may cause false positives. For example, updates may temporarily "fail" while files are moved around, but work fine once completed. Sending emails about temporary failures would just be confusing to the recipient.

Props Clorith, airamerica.
Fixes #48964.

git-svn-id: https://develop.svn.wordpress.org/trunk@47768 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-fatal-error-handler.php

@@ -30,6 +30,11 @@ class WP_Fatal_Error_Handler {
 			return;
 		}
 
+		// Do not trigger the fatal error handler while updates are being installed.
+		if ( wp_in_maintenance_mode() ) {
+			return;
+		}
+
 		try {
 			// Bail if no error found.
 			$error = $this->detect_error();