Use non-deprecated hook when possible

This brings the same change from this PR:
#31027 which may have missed
the deprecated hook in the refactor PR, since it hadn't landed yet.

lib/experiments-page.php

@@ -114,4 +114,9 @@ function gutenberg_experiments_editor_settings( $settings ) {
 	);
 	return array_merge( $settings, $experiments_settings );
 }
-add_filter( 'block_editor_settings', 'gutenberg_experiments_editor_settings' );
+// This can be removed when plugin support requires WordPress 5.8.0+.
+if ( function_exists( 'get_block_editor_settings' ) ) {
+	add_filter( 'block_editor_settings_all', 'gutenberg_experiments_editor_settings' );
+} else {
+	add_filter( 'block_editor_settings', 'gutenberg_experiments_editor_settings' );
+}