ALTER TABLE ALTER CONSTRAINT misleading error message

hi.

create table t(a int, constraint cc check(a = 1));
ALTER TABLE t ALTER CONSTRAINT cc not valid;
ERROR: FOREIGN KEY constraints cannot be marked NOT VALID
LINE 1: ALTER TABLE t ALTER CONSTRAINT cc not valid;
^

the error message seems misleading,
should we consider it as a bug for pg18?
the entry point is in gram.y, following part:

| ALTER CONSTRAINT name ConstraintAttributeSpec
{
AlterTableCmd *n = makeNode(AlterTableCmd);
ATAlterConstraint *c = makeNode(ATAlterConstraint);
n->subtype = AT_AlterConstraint;
n->def = (Node *) c;
c->conname = $3;
if ($4 & (CAS_NOT_ENFORCED | CAS_ENFORCED))
c->alterEnforceability = true;
if ($4 & (CAS_DEFERRABLE | CAS_NOT_DEFERRABLE |
CAS_INITIALLY_DEFERRED | CAS_INITIALLY_IMMEDIATE))
c->alterDeferrability = true;
if ($4 & CAS_NO_INHERIT)
c->alterInheritability = true;
processCASbits($4, @4, "FOREIGN KEY",
&c->deferrable,
&c->initdeferred,
&c->is_enforced,
NULL,
&c->noinherit,
yyscanner);
$$ = (Node *) n;
}