Override GITHUB_ACTIONS=0 for tidy tests

Author: Kobzol

src/bootstrap/src/core/build_steps/test.rs

@@ -3146,6 +3146,9 @@ impl Step for Distcheck {
             .run(builder);
         command(helpers::make(&builder.config.host_target.triple))
             .arg("check")
+            // Do not run the build as if we were in CI, otherwise git would be assumed to be
+            // present, but we build from a tarball here
+            .env("GITHUB_ACTIONS", "0")
             .current_dir(&plain_src_dir)
             .run(builder);