Remove arch from CI jobs and update actions

Specifying arch forces the macOS runner to run in emulation mode (the correct
arch is aarch64), making it much slower than it needs to be.

In the process, I also updated some actions and added dependabot to keep them updated

.github/dependabot.yml

@@ -0,0 +1,7 @@
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "weekly"

.github/workflows/ci.yml

@@ -27,19 +27,16 @@ jobs:
           - ubuntu-latest
           - macOS-latest
           - windows-latest
-        arch:
-          - x64
     steps:
       - uses: actions/checkout@v4
-      - uses: julia-actions/cache@v1
-      - uses: julia-actions/setup-julia@v1
+      - uses: julia-actions/cache@v2
+      - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.version }}
-          arch: ${{ matrix.arch }}
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
       - uses: julia-actions/julia-processcoverage@v1
-      - uses: codecov/codecov-action@v3
+      - uses: codecov/codecov-action@v4
         with:
           file: lcov.info
           token: ${{secrets.CODECOV_TOKEN}}