Delete newline that causes formatting issue on Github. (#9054)

* Disable mdformat on .github/pull_request_template.md

mdformat-gfm doesn't understand GitHub's checklists.
Opened hukkin/mdformat-gfm#58
---------

Co-authored-by: halide-ci[bot] <266445882+halide-ci[bot]@users.noreply.github.com>
Co-authored-by: Alex Reinking <areinking@adobe.com>

Author: 3 people

.github/pull_request_template.md

@@ -21,5 +21,5 @@ least be tagged with the `release_notes` label.
 - [ ] Documentation updated (if public API changed)
 - [ ] Python bindings updated (if public API changed)
 - [ ] Benchmarks are included here if the change is intended to affect
-  performance.
+      performance.
 - [ ] Commits include AI attribution where applicable (see Code of Conduct)

.pre-commit-config.yaml

@@ -85,6 +85,7 @@ repos:
           - mdformat-gfm
           - mdformat-ruff
           - mdformat-shfmt
+        exclude: ^.github/pull_request_template\.md$  # mdformat-gfm doesn't understand GitHub's checklists.
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
     rev: v0.15.5