Bump CI actions and drop hardcoded arch (#14)

Bumps julia-actions/setup-julia v2→v3, julia-actions/cache to v3 where
applicable, and codecov/codecov-action to v6 where applicable. Drops
the hardcoded arch: x64 from the matrix so setup-julia picks the
runner's native arch — matches the pattern used by the shared
ITensorActions/Tests.yml reusable workflow.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: mtfishman

.github/workflows/CI.yml

@@ -13,7 +13,7 @@ concurrency:
   cancel-in-progress: ${{ startsWith(github.ref, 'refs/pull/') }}
 jobs:
   test:
-    name: Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.arch }} - ${{ github.event_name }}
+    name: Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ github.event_name }}
     runs-on: ${{ matrix.os }}
     timeout-minutes: 60
     permissions: # needed to allow julia-actions/cache to proactively delete old caches that it has created
@@ -29,14 +29,11 @@ jobs:
           - ubuntu-latest
           - macOS-latest
           - windows-latest
-        arch:
-          - x64
     steps:
       - uses: actions/checkout@v6
-      - uses: julia-actions/setup-julia@v2
+      - uses: julia-actions/setup-julia@v3
         with:
           version: ${{ matrix.version }}
-          arch: ${{ matrix.arch }}
       - uses: julia-actions/cache@v3
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
@@ -55,7 +52,7 @@ jobs:
       statuses: write
     steps:
       - uses: actions/checkout@v6
-      - uses: julia-actions/setup-julia@v2
+      - uses: julia-actions/setup-julia@v3
         with:
           version: '1'
       - uses: julia-actions/cache@v3