The mergebasebranch option's base branch merge does not update submodules
So branches will build and run the test suite with the Git submodule state as if the base branch merge didn't happen, while Tails Git itself has the correct state.
feature/stretch as base branch. On May 5th we updated the Chutney submodule so Tor is not broken in the test suite. But when
feature/stretch (due to
mergebasebranch) it won't checkout the new Git submodule state, and that is why this branch still fails all tests using Tor.
Build system: also update submodules after merging the base branch.
... via the `mergebasebranch` build option.