Keep the cross test config from affecting other cross usage

Since we also use `cross` to build some of the releases.

Author: EliahKagan

Cross.toml renamed to etc/docker/test-cross.toml

@@ -1,3 +1,7 @@
+# `cross` configuration for running tests. Treated like `Cross.toml` if enabled
+# with `CROSS_CONFIG=etc/docker/test-cross.toml`. This avoids affecting other
+# `cross` usage, e.g. in `release.yml`. See `cross-test` recipes in `justfile`.
+
 [build.env]
 passthrough = [
     "CI",

justfile

@@ -231,7 +231,8 @@ cross-image target:
 
 # Test another platform with `cross`
 cross-test target: (cross-image target)
-    NO_PRELOAD_CXX=1 cross test --workspace --no-fail-fast --target "{{ target }}" \
+    CROSS_CONFIG=etc/docker/test-cross.toml NO_PRELOAD_CXX=1 \
+        cross test --workspace --no-fail-fast --target "{{ target }}" \
         --no-default-features --features max-pure \
         -- --skip realpath::fuzzed_timeout