servo: Merge #19856 - Use default sccache timeout (from servo:jdm-patch-6); r=jdm

Try to resolve the ongoing issues on cross builders where the sccache server takes up 50% of available memory.

Source-Repo: https://github.com/servo/servo
Source-Revision: caefaa79c9d3269b10464f17c3d991bd2c0f954e

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 2deba44596a4a3a88bffefda23652f3fef987cb1

servo/etc/ci/buildbot_steps.yml

@@ -3,6 +3,7 @@ env:
   CARGO_INCREMENTAL: "0"
   CCACHE: sccache
   RUSTC_WRAPPER: sccache
+  SCCACHE_IDLE_TIMEOUT: "600"
 
 mac-rel-wpt1:
   - ./mach clean-nightlies --keep 3 --force