Install pixi-diff-to-markdown via pixi

.github/workflows/update_pixi_lockfile.yml

@@ -23,13 +23,12 @@ jobs:
           run-install: false
 
       - name: Install pixi-diff-to-markdown
-        run: pip install pixi-diff-to-markdown
+        run: pixi global install pixi-diff-to-markdown
 
       - name: Update pixi lockfile and generate diff
         run: |
           set -o pipefail
-          pixi update --json --no-install
-          pixi-diff-to-markdown --explicit-column=true --hide=false > diff.md
+          pixi update --json --no-install | pixi exec pixi-diff-to-markdown --explicit-column=true --hide=false > diff.md
 
       - name: Configure Git for LFS
         run: |