Add cache-name to main example

This patch suggests to add `cache-name` to the main example since most Julia projects test multiple versions in a matrix.

README.md

@@ -19,10 +19,17 @@ permissions:
 jobs:
   test:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        version:
+          - '1.6'
+          - '1'
     steps:
       - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v2
       - uses: julia-actions/cache@v2
+        with:
+          cache-name: 'test-${{ matrix.os }}'
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
 ```