upgrade sccache-action to latest version (#390)

CI is broken currently, apparently because [email protected] is
using an azure service that was taken offline on april 15

Author: pchickey

.github/workflows/main.yml

@@ -20,7 +20,7 @@ jobs:
         echo "RUSTC_WRAPPER=sccache" >> $GITHUB_ENV
         echo "SCCACHE_GHA_ENABLED=true" >> $GITHUB_ENV
     - name: Run sccache-cache
-      uses: mozilla-actions/[email protected].4
+      uses: mozilla-actions/[email protected].8
     - name: Install Rust
       run: |
         rustup set profile minimal