ci: fix GitHub Actions workflow for Node.js 16+ compatibility

- Remove Node.js 14 from test matrix (reached EOL 2023-04-30)
- Set codecov fail_ci_if_error to false to prevent rate limit failures
- Resolves CI infrastructure issues documented in CI_FIX_GUIDE.md

Node.js 14 is no longer supported as current dependencies (xo@0.57)
require Node.js 15+ for ES2021 features (logical assignment operators).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/main.yml

@@ -12,7 +12,6 @@ jobs:
         node-version:
           - 18
           - 16
-          - 14
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
@@ -23,4 +22,4 @@ jobs:
       - uses: codecov/codecov-action@v2
         if: matrix.node-version == 16
         with:
-          fail_ci_if_error: true
+          fail_ci_if_error: false