test: keep the IBus startup check off a desktop's IBUS_ADDRESS_FILE

buildaddrpath honours IBUS_ADDRESS_FILE, so under an IBus session the
ownership check looked at the live address file and failed.

tests/ibus_test.c

@@ -95,6 +95,8 @@ ibus_startup_requires_ownership(struct ct *t)
 	saved = old == nil ? nil : strdup(old);
 	if(old != nil && !CT_CHECK(t, saved != nil))
 		return;
+	/* An IBus desktop names a live address file; the path must be ours. */
+	unsetenv("IBUS_ADDRESS_FILE");
 	if(!CT_CHECK(t, mkdtemp(root) != nil))
 		goto cleanup;
 	made = 1;