test: pin the no-candidate host test against real group membership

The remediation-message test relied on the runner not being in group
'party'; on boxes where the runner is (the deployment hosts), host
succeeded and the test failed. Route the child's id(1) through the
suite's stub so the caller is deterministically in no candidate group.

tests/45-group-select.bats

@@ -76,6 +76,7 @@ stub_id_groups() {
 }
 
 @test "host in no candidate group gets the remediation message" {
+  stub_id_groups "$USER dialout"
   unset TMUX_PARTY_GROUP
   export PARTY_GROUP_CANDIDATES="no-such-group-xyzzy"
   run "$PARTY_BIN" host nogroup