gotestsum reports TestMain when it fails but not when it passes

I have a test package which has a `TestMain` function, and I've tried to use `gotestsum --junitfile report.xml` to run it. However, I've observed the behavior for the `TestMain` JUnit result is different when it passes and fails.

1. When the `TestMain` fails, the `report.xml` file has a `TestMain` test case failure.
```
func TestMain(m *testing.M) {
log.Fatal("fatal")
os.Exit(m.Run())
}
```

2. When the `TestMain` passes, the `report.xml` file does not have a `TestMain` test case pass.
```
func TestMain(m *testing.M) {
os.Exit(m.Run())
}
```

It'll make more sense to always have `TestMain` as one test case in the JUnit result, regardless whether it passes or not.

Reproduce the issue with the two TestMain examples and compare the generated report.xml files. Trace the JUnit result generation path for TestMain, then verify that a passing TestMain produces a test case as well as a failing one.

Written by the indexing model from the issue text.