Eval opam env in flambda CI job.

.gitlab-ci.yml

@@ -42,6 +42,7 @@ build-coq.8.8.1-flambda:
     export OPAMROOT="$(pwd)/opamroot";
     export OPAMJOBS="$((2*$CPU_CORES))";
     export OPAM_EDITOR="$(which false)";
+    eval `opam conf env`;
     opam switch create "4.07.0+flambda"
   - git clone https://gitlab.mpi-sws.org/FP/iris-ci.git ci -b opam2
   - ci/buildjob