Pins peter-evans/create-pull-request to SHA

Pins peter-evans/create-pull-request to v8.1 commit hash instead of the
tag.

Author: Alex-Welsh

.github/workflows/update-overcloud-host-image-tags.yml

@@ -45,7 +45,7 @@ jobs:
         if: "${{ inputs.ubuntu_noble_tag != '' }}"
 
       - name: Propose changes via PR if required
-        uses: peter-evans/create-pull-request@v8
+        uses: peter-evans/create-pull-request@8170bccad11c0df62542c04dcaefe36d342dfd39
         with:
           path: ${{ github.workspace }}/src/kayobe-config
           commit-message: >-