Merge bitcoin/bitcoin#33138: ci: Pass CI_FAILFAST_TEST_LEAVE_DANGLING into container

fa1d2f6380 ci: Pass CI_FAILFAST_TEST_LEAVE_DANGLING into container (MarcoFalke)

Pull request description:

  After commit fd813bf863, the env var `CI_FAILFAST_TEST_LEAVE_DANGLING` is no longer passed into the container.

  This is harmless, because it isn't needed for the Linux containers and macos doesn't use containers at all.

  However, it would be nice to document it as an allowed setting and consistently pass it on, when set. So do that here.

ACKs for top commit:
  fanquake:
    ACK fa1d2f6380

Tree-SHA512: b61780a27f4c2e11359827b1360a34a132e15bff94f358cbf4d453805afcafb873e2c395908b17610fae026ead93226c19a8f6be40fbb87b623ee992f3e2b43e

ci/test/02_run_container.py

@@ -26,9 +26,12 @@ def main():
         encoding="utf8",
     ).stdout.splitlines()
     settings = set(l.split("=")[0].split("export ")[1] for l in settings)
-    # Add this one manually, because it is the only one set inside the
-    # container that also allows external overwrites
-    settings.add("BASE_BUILD_DIR")
+    # Add "hidden" settings, which are never exported, manually. Otherwise,
+    # they will not be passed on.
+    settings.update([
+        "BASE_BUILD_DIR",
+        "CI_FAILFAST_TEST_LEAVE_DANGLING",
+    ])
 
     # Append $USER to /tmp/env to support multi-user systems and $CONTAINER_NAME
     # to allow support starting multiple runs simultaneously by the same user.