Use opam to execute commands under the opam environment

Author: andersfugmann

.github/workflows/workflow.yml

@@ -37,8 +37,7 @@ jobs:
 
       - run: |
           opam install . --deps-only --with-doc --with-test
-          eval $(opam env)
-          dune runtest
+          opam exec -- dune runtest
 
       - run: |
           for package in ${{ matrix.packages }}; do