[CI][Github] Set SCCACHE_IDLE_TIMEOUT to 0 (#150508)
This patch sets the sccache idle timeout to zero which ensures that it
will run indefinitely. Without this, sccache will sometimes stop when
several long test suites get run consequitively. This resets the
statistics which we save at the end. Ensuring the process stays running
means we have accurate statistics when we collect them at the end.
