Include `file` and `line` attribute for testcases

[hanikesn]

We're using go-junit-report together with action-junit-report in order to report and annotate our Github PR's with test failures. Unfortunately they don't show up inline the PR as it needs the filename and line number for that:

• https://github.com/mikepenz/action-junit-report/blob/5f36538697142e07cd2e6a7016f10d2be65be747/src/testParser.ts#L451-L456

It'd be nice to include that information in the output as well.

[lsgndln]

I would be interested as well :)