Fix format-pr workflow permissions for creating PRs (#52)

Add explicit contents:write and pull-requests:write permissions to the
format-pr workflow job. The default GITHUB_TOKEN now has read-only
permissions, causing the peter-evans/create-pull-request action to fail
with a 403 when pushing the formatting branch.

Co-authored-by: ChrisRackauckas-Claude <noreply@anthropic.com>
Co-authored-by: Chris Rackauckas <accounts@chrisrackauckas.com>

Author: 3 people

.github/workflows/FormatPR.yml

@@ -5,6 +5,9 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
     steps:
       - uses: actions/checkout@v4
       - name: Install JuliaFormatter and format