Update GitHub Actions

Signed-off-by: Sora Morimoto <[email protected]>

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: weekly

.github/workflows/main.yml

@@ -1,4 +1,4 @@
-name: Main workflow
+name: Builds, tests & co
 
 on:
   pull_request:
@@ -7,29 +7,30 @@ on:
     # Prime the caches every Monday
     - cron: 0 1 * * MON
 
+permissions: read-all
+
 jobs:
   build:
     strategy:
       fail-fast: false
       matrix:
         os:
           - macos-latest
+          - ubuntu-latest
           - windows-latest
         ocaml-compiler:
-          - 4.13.x
+          - "5"
+          - "4"
 
     runs-on: ${{ matrix.os }}
 
     steps:
-      - name: Checkout code
-        uses: actions/checkout@v2
+      - name: Checkout tree
+        uses: actions/checkout@v4
 
-      - name: Use OCaml ${{ matrix.ocaml-compiler }}
-        uses: ocaml/setup-ocaml@v2
+      - name: Set-up OCaml
+        uses: ocaml/setup-ocaml@v3
         with:
-          opam-repositories: |
-            opam-repository-mingw: https://github.com/ocaml-opam/opam-repository-mingw.git#sunset
-            default: https://github.com/ocaml/opam-repository.git
           ocaml-compiler: ${{ matrix.ocaml-compiler }}
 
       - run: opam install . --deps-only --with-test