CI: get rid of the Node.js warnings

Node.js 16 actions are deprecated.  We need to bump the following
actions:

  -  julia-actions/setup-julia (to v2)
  -  julia-actions/cache (to ???)
  -  codecov/codecov-action (to v4)

Within this commit, a Codecov token has been added to the github
secrets.

.github/workflows/ci.yml

@@ -30,14 +30,15 @@ jobs:
           - x86
     steps:
       - uses: actions/checkout@v4
-      - uses: julia-actions/setup-julia@v1
+      - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
       - uses: julia-actions/cache@v1
       - 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:
+          token: ${{ secrets.CODECOV_TOKEN }}
           files: lcov.info