Explicitly unset RUSTC_WRAPPER=sccache environment variable (#12771)

* CI: Explicitly unset RUSTC_WRAPPER=sccache environment variable

* Try with `rusty-cachier` disabled

* Re-enable `rusty-cachier` and try with the staging image

* Bring back `production` image

* Sort crates before splitting them into groups (+ some improvements) (#12755)

* sort crates before splitting them into groups

this is useful so that crates always get routed to a specific group for a given version of the source code, which means that jobs for each batch can be reliably retried individually

* more verbose output

* misc improvements

* put uniq after sort

uniq filters by adjacent lines

* shellcheck

* rm useless backlashes

* handle edge case of no crates detected

* Revert "Sort crates before splitting them into groups (+ some improvements) (#12755)"

This reverts commit fde839183a12a2bd51efc7143ebcddeed81ea6fa.

Co-authored-by: João Paulo Silva de Souza <[email protected]>