tests/Makefile.include: Fix 'make check-help' output

tests/Makefile.include: Fix 'make check-help' output

Since commit 3d2f73ef75e ("build: use "meson test" as the test harness"),
check-report.tap is no more, and we have check-report.junit.xml.

Update the output of 'make check-help', which was still listing
'check-report.tap', accordingly.

Fixes: 3d2f73ef75e
Signed-off-by: Dario Faggioli <dfaggioli@suse.com>
Message-Id: <165366545439.6869.11633009118019728798.stgit@work>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>