Fix: Force-add ignored docs in release branch workflows (llm-d#293)

The preview/docs directory is in .gitignore for main branch, but needs
to be committed in release branches. Use 'git add -f' to force-add
these files in both create-release-branch and sync-release-docs workflows.

Fixes workflow failure when creating release branches.

Signed-off-by: Carlos H. Andrade Costa <chcost@us.ibm.com>

Author: chcost

.github/workflows/create-release-branch.yml

@@ -52,7 +52,7 @@ jobs:
 
       - name: Commit synced docs
         run: |
-          git add preview/docs preview/static/img/docs
+          git add -f preview/docs preview/static/img/docs
           if ! git diff --staged --quiet; then
             git commit -m "Initial docs sync from llm-d/llm-d@${{ inputs.source_branch }}"
           else

.github/workflows/sync-release-docs.yml

@@ -81,7 +81,7 @@ jobs:
             cd ..
 
             # Commit changes if any
-            git add preview/docs preview/static/img/docs
+            git add -f preview/docs preview/static/img/docs
             if ! git diff --staged --quiet; then
               COMMIT_MSG="Nightly docs sync from llm-d/llm-d@${SOURCE_BRANCH}