Change default branch from 'main' to 'master' in docs

Author: michel2323

.github/workflows/docs.yml

@@ -3,7 +3,7 @@ name: Documentation
 on:
   push:
     branches:
-      - main
+      - master
     tags: '*'
   pull_request:
     types: [opened, synchronize, reopened]
@@ -26,4 +26,4 @@ jobs:
           version: 'lts'
       - uses: julia-actions/cache@v2
       - uses: julia-actions/julia-buildpkg@latest
-      - run: julia --project=docs/ docs/make.jl
+      - run: julia --project=docs/ docs/make.jl