fix(backend): SQLのサニタイズを強化 (#14920)

* Fix code scanning alert no. 28: Incomplete string escaping or encoding (MisskeyIO#800)

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>
(cherry picked from commit 443335c662b14f609d6a81a8f3807e95709aebc1)

* ✌️

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Co-authored-by: あわわわとーにゅ <17376330+u1-liquid@users.noreply.github.com>

packages/backend/src/misc/sql-like-escape.ts

@@ -4,5 +4,5 @@
  */
 
 export function sqlLikeEscape(s: string) {
-	return s.replace(/([%_])/g, '\\$1');
+	return s.replace(/([\\%_])/g, '\\$1');
 }