Mock methods with mixed return type

[ghostwriter]

This patch resolves #1149, via the following changes:

• Add tests and fixtures
• Mock methods with mixed return type.

class MockingMethodsWithMixedReturnTypeTest extends MockeryTestCase
{
    public function testMockingMixedReturnType()
    {
        $mock = \Mockery::mock(MyInterface::class);
        $mock->shouldReceive("foo->bar")->andReturn("bar");
        $this->assertSame('bar', $mock->foo()->bar());
    }
}

interface MyInterface {
    public function getFoo(): mixed;
}

[davedevelopment]

Thank you!