ci: check editor-check formatting in the product check

Every product adds a fixture to tools/editor-check, but only the CI
previews job checked its formatting, so an unformatted fixture passed
the local product check and failed CI.

scripts/check-plugin.py

@@ -15,6 +15,8 @@ commands = [
     ["cargo", "test", *packages, "--locked"],
     ["cargo", "clippy", *packages, "--all-targets", "--locked", "--", "-D", "warnings"],
     ["cargo", "fmt", "--manifest-path", product["manifest"], "--", "--check"],
+    # Every product has a fixture in the editor renderer; CI checks its formatting too.
+    ["cargo", "fmt", "--manifest-path", "tools/editor-check/Cargo.toml", "--", "--check"],
     ["cargo", "test", "--manifest-path", product["manifest"], "--locked"],
     ["cargo", "clippy", "--manifest-path", product["manifest"], "--all-targets", "--locked", "--", "-D", "warnings"],
 ]