ci: fix some github actions warnings (argoproj#2375)

* bump codecov/codecov-action: v2 to v3

The codecov/codecov-action api didn't change with v3.
Node.js version was updated from 12 to 16, fixing deprecation warning.

See: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/

Signed-off-by: Thomas Riccardi <[email protected]>

* explain why we can't use native actions/download-artifact: we get artifacts from another workflow

Signed-off-by: Thomas Riccardi <[email protected]>

* fix publish test result warning

since v2 of EnricoMi/publish-unit-test-result-action:
warning:
Option FILES is deprecated, please use JUNIT_FILES instead!

all files are junit format, and are all named junit.xml

Signed-off-by: Thomas Riccardi <[email protected]>

Signed-off-by: Thomas Riccardi <[email protected]>

.github/workflows/e2e-test-results.yml

@@ -1,3 +1,4 @@
+# use separate workflow to support fork repositories and dependabot branches when publishing test results: see https://github.com/EnricoMi/publish-unit-test-result-action#support-fork-repositories-and-dependabot-branches
 name: Test Results
 
 on:
@@ -18,6 +19,7 @@ jobs:
       actions: read
     steps:
       - name: Download and Extract Artifacts
+        # TODO repace with native actions/download-artifact once it supports downloading from another workflow: https://github.com/actions/download-artifact/issues/3
         env:
           GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
         run: |
@@ -37,7 +39,7 @@ jobs:
           commit: ${{ github.event.workflow_run.head_sha }}
           event_file: artifacts/Event File/event.json
           event_name: ${{ github.event.workflow_run.event }}
-          files: "artifacts/**/*.xml"
+          junit_files: "artifacts/**/junit.xml"
           compare_to_earlier_commit: false
           test_changes_limit: 0
           fail_on: "errors"