ci/tumbleweed: disable sanitizers for GCC build

It produces some bogus warnings when UBSAN is enabled:
../demux/demux_mf.c:103:22: error: ‘%s’ directive argument is null [-Werror=format-overflow=]

Which is clearly not possible at this point.

ci/build-tumbleweed.sh

@@ -4,7 +4,7 @@ set -e
 . ./ci/build-common.sh
 
 meson setup build $common_args $@ \
-  -Db_sanitize=address,undefined \
+  -Db_sanitize=$([ "$CC" = "gcc" ] && echo none || echo address,undefined) \
   -Dcdda=enabled \
   -Ddvbin=enabled \
   -Ddvdnav=enabled \