Fix issue where users may not follow links to private messages they belong to (#26001)

* Fix issue where users may not follow links to private messages they belong to

* Update tests

server/channels/api4/post_test.go

@@ -3992,6 +3992,12 @@ func TestPostReminder(t *testing.T) {
 func TestPostGetInfo(t *testing.T) {
 	th := Setup(t).InitBasic()
 	defer th.TearDown()
+
+	defer th.RestoreDefaultRolePermissions(th.SaveDefaultRolePermissions())
+	th.RemovePermissionFromRole(model.PermissionManagePrivateChannelMembers.Id, model.SystemUserRoleId)
+	th.RemovePermissionFromRole(model.PermissionManagePrivateChannelMembers.Id, model.ChannelUserRoleId)
+	th.RemovePermissionFromRole(model.PermissionManagePrivateChannelMembers.Id, model.TeamUserRoleId)
+
 	client := th.Client
 	sysadminClient := th.SystemAdminClient
 	sysadminClient.AddTeamMember(context.Background(), th.BasicTeam.Id, th.SystemAdminUser.Id)