ci: Pass CI_FAILFAST_TEST_LEAVE_DANGLING into container #33138

After commit fd813bf863b1ffa91429de6342285b35bab2bfa4, 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.

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For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33138.

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ACK fa1d2f63803e71d21b470cf4eb52fbe941aa0b28