mtest: add an ASCII-only version of the spinner
mtest: add an ASCII-only version of the spinner

While the horizontal line and the other pictograms in mtest have an ASCII-only
version, the spinner does not.  This causes mtest to fail with a
UnicodeEncodeError exception on non-Unicode locales.

Fixes: #9538
Signed-off-by: Paolo Bonzini <69d3ebcf5ee4e7f05a50dc23cd96655b730804b4@redhat.com>

pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson