try to use julia 1.9 for docs build

.github/workflows/docs.yml

@@ -14,7 +14,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: julia-actions/setup-julia@v1
         with:
-          version: 1.10
+          version: 1.9
       - name: Install dependencies
         run: julia --project=docs -e 'using Pkg; Pkg.instantiate()'
       - name: Build and deploy