message: Fix a grammatical error in the PR template
  Original commit:
diff: Please include the following checklist in your PR:
  - [ ] The documentation has been updated if necessary.
  -- [ ] All code conforms to the [Rust](https://github.com/luna/enso/blob/main/docs/style-guide/rust.md).
  +- [ ] All code conforms to the [Rust](https://github.com/luna/enso/blob/main/docs/style-guide/rust.md) style guide.
  - [ ] All code has been tested where possible.
  - [ ] All code has been profiled where possible.
  