"No loader is configured" when using glob entrypoints with plugins

[SystemParadox]

See failing test case at https://github.com/SystemParadox/esbuild/tree/issue-plugin-glob-entrypoint.

This test works if the entrypoint is changed to in.json5, but using any kind of glob entrypoint results in:

✘ [ERROR] No loader is configured for ".json5" files