Revert "Bump mhausenblas/mkdocs-deploy-gh-pages from 1.18 to 1.19"

This reverts commit f326067a526963e76fb80de21e6c99f6e795f342.

Reason for revert: There is an issue which breaks the deployment.

Change-Id: Idef551b910a115c4db08492f59e3ce75c17d35bd
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index a70c656..b103cf1 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -15,6 +15,6 @@
           fetch-depth: 0
 
       - name: Deploy docs
-        uses: mhausenblas/mkdocs-deploy-gh-pages@1.19
+        uses: mhausenblas/mkdocs-deploy-gh-pages@1.18
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}