Exclude companion object from report if it contains only constants

[shanshin]

Describe the bug
Same as for regular object, companion object with only should be excluded from report

Expected behavior
MyInterface should be excluded from report

Reproducer

interface MyInterface {
    companion object {
        const val constant = "foo"
    }
}

Reports

Environment

• Kover Gradle Plugin version: 0.7.6, 0.8.0-Beta