CI: Update to CompatHelper v3

.github/workflows/CompatHelper.yml

@@ -3,16 +3,35 @@ on:
   schedule:
     - cron: 0 0 * * *
   workflow_dispatch:
+permissions:
+  contents: write
+  pull-requests: write
 jobs:
   CompatHelper:
     runs-on: ubuntu-latest
     steps:
+      - name: Check if Julia is already available in the PATH
+        id: julia_in_path
+        run: which julia
+        continue-on-error: true
+      - name: Install Julia, but only if it is not already available in the PATH
+        uses: julia-actions/setup-julia@v1
+        with:
+          version: '1'
+          arch: ${{ runner.arch }}
+        if: steps.julia_in_path.outcome != 'success'
+      - name: "Add the General registry via Git"
+        run: |
+          import Pkg
+          ENV["JULIA_PKG_SERVER"] = ""
+          Pkg.Registry.add("General")
+        shell: julia --color=yes {0}
       - name: "Install CompatHelper"
         run: |
           import Pkg
           name = "CompatHelper"
           uuid = "aa819f21-2bde-4658-8897-bab36330d9b7"
-          version = "2"
+          version = "3"
           Pkg.add(; name, uuid, version)
         shell: julia --color=yes {0}
       - name: "Run CompatHelper"