CI: github actions: use cache for OpenTracing

this caches OpenTracing libs between builds, should save couple of minutes
for each build.

(cherry picked from commit b9e3fb7315e32cee678d3635f715de65b6c53fae)
Signed-off-by: William Lallemand <wlallemand@haproxy.org>
(cherry picked from commit 4de35027d01617fcbd928f5b27132d46d0017cd6)
Signed-off-by: William Lallemand <wlallemand@haproxy.org>
2 files changed