support --show-capture with --tb=line

[zaplapl]

closes #13865 by duplicating self._outrep_summary(rep) invocation during summary_failures_combined

considered refactoring into something like:

        for rep in reports:
            self._outrep_summary(rep)
                if style == "line":
                        line = self._getcrashline(rep)
                        self.write_line(line)
                else:
                        msg = self._getfailureheadline(rep)
                        self.write_sep("_", msg, red=True, bold=True)
                        self._handle_teardown_sections(rep.nodeid)

to avoid committing too hard to the branching logic in the code

but submitting this commit instead since it has fewer side-effects

[nicoddemus]

Thanks @zaplapl for the PR, please take a look at my comments.

[nicoddemus]

LGTM, thanks!