Fix codecov upload condition in CI workflow

The upload condition used 'discard' which never matches any matrix
value, preventing coverage data from being uploaded. Changed to 'ubuntu'
to match the actual os-type matrix value.

Author: etr

.github/workflows/verify-build.yml

@@ -669,4 +669,4 @@ jobs:
       run: |
         cd build ;
         bash <(curl -s https://codecov.io/bash) ;
-      if: ${{ matrix.os-type == 'discard' && matrix.c-compiler == 'gcc' && matrix.debug == 'debug' && matrix.coverage == 'coverage' && success() }}
+      if: ${{ matrix.os-type == 'ubuntu' && matrix.c-compiler == 'gcc' && matrix.debug == 'debug' && matrix.coverage == 'coverage' && success() }}