SELECT Id, ProcessInstance.TargetObjectId
       FROM ProcessInstanceWorkitem
USING SCOPE Mine_And_My_Groups
      WHERE ProcessInstance.Status = 'Pending'
             AND ProcessInstance.ProcessDefinition.TableEnumOrId IN ('Account', 'Contact')

System.UnexpectedException: Illegal filter on ProcessInstanceWorkitem

@IsTest
static void testAsAdmin() {

    User u = getTestUser([SELECT Id FROM Profile WHERE Name = 'System Administrator'][0].Id);

    System.runAs(u) {
        //SUCCEEDS
        List<ProcessInstanceWorkitem> workitems = [
                SELECT Id, ProcessInstance.TargetObjectId
                FROM ProcessInstanceWorkitem
                USING SCOPE Mine_And_My_Groups
                WHERE ProcessInstance.Status = 'Pending'
                AND ProcessInstance.ProcessDefinition.TableEnumOrId IN ('Account', 'Contact')
        ];
    }
}

@IsTest
static void testAsStandardUser() {

    User u = getTestUser([SELECT Id FROM Profile WHERE Name = 'Standard User'][0].Id);

    System.runAs(u) {

        //FAILS
        List<ProcessInstanceWorkitem> workitems = [
                SELECT Id, ProcessInstance.TargetObjectId
                FROM ProcessInstanceWorkitem
                USING SCOPE Mine_And_My_Groups
                WHERE ProcessInstance.Status = 'Pending'
                AND ProcessInstance.ProcessDefinition.TableEnumOrId IN ('Account', 'Contact')
        ];
    }
}

static User getTestUser(Id profileId) {
    return new User(
            Alias = 'test',
            Email = 'exampletestuser@example.com',
            EmailEncodingKey = 'UTF-8',
            FirstName = 'Testing',
            LastName = 'Testing',
            LanguageLocaleKey = 'en_US',
            TimeZoneSidKey = 'America/Los_Angeles',
            LocaleSidKey = 'en_US',
            UserName = 'exampletestuser@example.com',
            ProfileId = profileId
    );
}