attempting to checkout the correct branch first

This commit attempts to update the (malicious) unicode detection workflow to fix an error on diff

 * #90
 * https://github.com/BusKill/buskill-app/actions/runs/10290611003/job/28481143563?pr=90

  2024-08-07T19:38:13.0639703Z + git branch -a
  2024-08-07T19:38:13.0661153Z * master
  2024-08-07T19:38:13.0662070Z   remotes/origin/HEAD -> origin/master
  2024-08-07T19:38:13.0662923Z   remotes/origin/dev
  2024-08-07T19:38:13.0663562Z   remotes/origin/font_setting
  2024-08-07T19:38:13.0664273Z   remotes/origin/gh-pages
  2024-08-07T19:38:13.0665072Z   remotes/origin/master
  2024-08-07T19:38:13.0665603Z   remotes/origin/v0.1.0
  2024-08-07T19:38:13.0666164Z   remotes/origin/v0.2.0
  2024-08-07T19:38:13.0666849Z   remotes/origin/v0.2.1
  2024-08-07T19:38:13.0667376Z   remotes/origin/v0.3.0
  2024-08-07T19:38:13.0667958Z   remotes/origin/v0.3.1
  2024-08-07T19:38:13.0668493Z   remotes/origin/v0.4.0
  2024-08-07T19:38:13.0668961Z   remotes/origin/v0.5.0
  2024-08-07T19:38:13.0669349Z   remotes/origin/v0.6.0
  2024-08-07T19:38:13.0670119Z   remotes/origin/v0.7.0
  ...
  2024-08-07T19:38:13.1733843Z ++ git diff --unified=0 924ca98 43dfed1
  2024-08-07T19:38:13.1734022Z ++ grep -Ev '^(--- a/|\+\+\+ b/)'
  2024-08-07T19:38:13.1734246Z fatal: bad object 43dfed1
  2024-08-07T19:38:13.1734418Z ++ grep -E '^[+]'
  2024-08-07T19:38:13.1734545Z + diff=
  2024-08-07T19:38:13.1734685Z + '[' 1 -ne 0 ']'
  2024-08-07T19:38:13.1734986Z + human_result='WARNING: git diff failed!'
  2024-08-07T19:38:13.1735154Z + echo 'WARNING: git diff failed!'
  2024-08-07T19:38:13.1735292Z + exit 1

Since it says there was a "bad object" -- let's try changing to the correct branch first

Author: maltfield

.github/workflows/unicode_warn.yml

@@ -43,6 +43,7 @@ jobs:
         set -x
         git config --global --add safe.directory .
         git config --global --add safe.directory "$(pwd)"
+        git checkout ${{ github.event.pull_request.head.ref }}
         git branch -a
         git log