Address PreparedSQL lints in Db

The WPCS PreparedSQL lints are unable to work
with variables. They require either refactoring
to run everything inline or ignoring the linter.

Refactor the SHOW INDEX query to be all inline.
Ignore the linter for other calls since it's
impossible to write them inline.

I reviewed all callers to confirm that they
already prepare the SQL properly.

Author: john-shaffer

src/Db.php

@@ -34,13 +34,18 @@ public static function ensureIndex(
     ): bool {
         global $wpdb;
 
-        $query = $wpdb->prepare(
-            "SHOW INDEX FROM $table_name WHERE key_name = %s",
-            $index_name
+        $indexes = $wpdb->query(
+            $wpdb->prepare(
+                'SHOW INDEX FROM %i WHERE key_name = %s',
+                $table_name,
+                $index_name,
+            ),
         );
-        $indexes = $wpdb->query( $query );
 
         if ( 0 === $indexes ) {
+            // Ignore prepare rule because the query has already
+            // been prepared by the caller.
+            // phpcs:ignore WordPress.DB.PreparedSQL
             $result = $wpdb->query( $create_index_sql );
             if ( false === $result ) {
                 WsLog::l( "Failed to create $index_name index on $table_name." );
@@ -90,6 +95,9 @@ public static function query(
     ): int|bool {
         global $wpdb;
 
+        // Ignore prepare rule because the query has already
+        // been prepared by the caller.
+        // phpcs:ignore WordPress.DB.PreparedSQL
         $result = $wpdb->query( $query );
         if ( $result !== false ) {
             return $result;