Issue #3414521 by LOBsTerr: Update validation messages

src/Plugin/Validation/Constraint/PreventDuplicatedConstraintValidator.php

@@ -74,7 +74,7 @@ class PreventDuplicatedConstraintValidator extends ConstraintValidator implement
         // Check if user already a member.
         $membership = $this->groupMembershipLoader->load($group, $user);
         if (!empty($membership)) {
-          $this->context->addViolation($this->t('User with such email already a member of @group.', ['@group' => $group->label()]));
+          $this->context->addViolation($this->t('User with such email is already a member of @group.', ['@group' => $group->label()]));
           return;
         }
       }
@@ -87,7 +87,7 @@ class PreventDuplicatedConstraintValidator extends ConstraintValidator implement
       // if user was invited using entity reference field.
       $membership = $this->groupMembershipLoader->load($group, $invitee);
       if (!empty($membership)) {
-        $this->context->addViolation($this->t('User with such email already a member of @group.', ['@group' => $group->label()]));
+        $this->context->addViolation($this->t('User is already a member of @group.', ['@group' => $group->label()]));
         return;
       }