Revert "Use coveralls instead of codecov"

This reverts commit bbb3721540.

.github/workflows/test.yaml

@@ -26,3 +26,9 @@ jobs:
         uses: coverallsapp/github-action@v1.1.2
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
+      - uses: codecov/codecov-action@v1
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }} # not required for public repos
+          file: ./coverage.txt # optional
+          flags: unittests # optional
+          fail_ci_if_error: false # optional (default = false)

codecov.yaml

@@ -0,0 +1,13 @@
+comment: no # do not comment PR with the result
+
+coverage:
+  range: 50..90 # coverage lower than 50 is red, higher than 90 green, between color code
+
+  status:
+    project: # settings affecting project coverage
+      default:
+        target: auto # auto % coverage target
+        threshold: 5%  # allow for 5% reduction of coverage without failing
+
+    # do not run coverage on patch nor changes
+    patch: false