set Vault namespace from task in vault_hook JWT login (#19080)

The JWT login codepath for the `vault_hook` was missing the Vault namespace, so
the login request for non-default namespaces would fail.

client/allocrunner/taskrunner/vault_hook.go

@@ -431,8 +431,9 @@ func (h *vaultHook) deriveVaultTokenJWT() (string, error) {
 
 	// Derive Vault token with signed identity.
 	token, err := h.client.DeriveTokenWithJWT(h.ctx, vaultclient.JWTLoginRequest{
-		JWT:  signed.JWT,
-		Role: role,
+		JWT:       signed.JWT,
+		Role:      role,
+		Namespace: h.vaultBlock.Namespace,
 	})
 	if err != nil {
 		return "", structs.WrapRecoverable(