Fix repository capitalization in deploy_guide.yml.

This check must be case-insensitive, because it's been working with
`rust-gpu` even though the repository owner is actually `Rust-GPU`.

Author: nnethercote

.github/workflows/deploy_guide.yml

@@ -12,7 +12,7 @@ concurrency:
 jobs:
   deploy:
     # Only run on the main repository, not on forks
-    if: github.repository == 'rust-gpu/Rust-CUDA'
+    if: github.repository == 'Rust-GPU/rust-cuda'
     runs-on: ubuntu-latest
     environment:
       name: github-pages