CI: use free runners for x86_64-gnu-tools and x86_64-rust-for-linux

Author: marcoieni

src/ci/github-actions/jobs.yml

@@ -232,7 +232,7 @@ auto:
   # Tests integration with Rust for Linux.
   # Builds stage 1 compiler and tries to compile a few RfL examples with it.
   - image: x86_64-rust-for-linux
-    <<: *job-linux-8c
+    <<: *job-linux-4c
 
   - image: x86_64-gnu
     <<: *job-linux-4c
@@ -280,7 +280,7 @@ auto:
   - image: x86_64-gnu-tools
     env:
       DEPLOY_TOOLSTATES_JSON: toolstates-linux.json
-    <<: *job-linux-8c
+    <<: *job-linux-4c
 
   ####################
   #  macOS Builders  #