Fix gosec, govet, and errorlint linter errors

Co-authored-by: Junie <junie@jetbrains.com>

internal/barrier/barrier.go

@@ -39,8 +39,8 @@ type Barrier interface {
 // AESGCMBarrier implements Barrier using AES-256-GCM encryption.
 type AESGCMBarrier struct {
 	db  *sql.DB
+	mek []byte
 	mu  sync.RWMutex
-	mek []byte // nil when sealed
 }
 
 // NewAESGCMBarrier creates a new AES-GCM barrier backed by the given database.
@@ -151,7 +151,7 @@ func (b *AESGCMBarrier) List(ctx context.Context, prefix string) ([]string, erro
 	if err != nil {
 		return nil, fmt.Errorf("barrier: list %q: %w", prefix, err)
 	}
-	defer rows.Close()
+	defer func() { _ = rows.Close() }()
 
 	var paths []string
 	for rows.Next() {