Merge pull request #40 from rust-lang/other-ci-improvements

Another batch of CI improvements

Author: pietroalbini

.github/workflows/main.yml

@@ -1,6 +1,12 @@
 name: CI
 
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - "**"
 
 jobs:
 

tests/utils/mod.rs

@@ -22,6 +22,11 @@ pub(crate) fn init_named_workspace(name: &str) -> Result<Workspace, Error> {
         builder = builder.running_inside_docker(true);
     }
 
+    #[cfg(linux)]
+    {
+        builder = builder.sandbox_image(rustwide::cmd::SandboxImage::remote("ubuntu:latest")?);
+    }
+
     Ok(builder.init()?)
 }