Update the actual workflow

Author: jwodder

.github/workflows/build-macos.yaml

@@ -397,8 +397,8 @@ jobs:
       - name: Set up environment
         run: |
           brew install exempi  # Needed by python-xmp-toolkit
-          mkdir -p ~/DLTMP
-          echo TMPDIR="$HOME"/DLTMP >> "$GITHUB_ENV"
+          mkdir -p /tmp/DLTMP
+          echo TMPDIR=/tmp/DLTMP >> "$GITHUB_ENV"
           git config --global user.email "test@github.land"
           git config --global user.name "GitHub Almighty"