Merge branch 'jk/test-lint-forbid-when-finished-in-subshell' into maint

Because "test_when_finished" in our test framework queues the clean-up tasks to be done in a shell variable, it should not be used inside a subshell. Add a mechanism to allow 'bash' to catch such uses, and fix the ones that were found. * jk/test-lint-forbid-when-finished-in-subshell: test-lib-functions: detect test_when_finished in subshell t7800: don't use test_config in a subshell test-lib-functions: support "test_config -C <dir> ..." t5801: don't use test_when_finished in a subshell t7610: don't use test_config in a subshell