Create dependabot.yml and update action versions (#31)

From https://discourse.julialang.org/t/psa-use-dependabot-to-update-github-actions-automatically/96001

Author: abhro

.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: "monthly"

.github/workflows/CI.yml

@@ -41,19 +41,18 @@ jobs:
           - x64
           - x86
         exclude:
-          # Test 32-bit only on Linux
           - os: macOS-latest
             arch: x86
     steps:
-      - uses: actions/checkout@v4
-      - uses: julia-actions/setup-julia@v1
+      - uses: actions/checkout@v5
+      - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
-      - uses: julia-actions/cache@v1
+      - uses: julia-actions/cache@v2
       - 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@v5
         with:
           files: lcov.info