Is that the same reason why we see
https://ci.debian.net/packages/r/rust-async-broadcast/testing/riscv64/ being retried over and over again without progress?
In contrast to the rust-gtk5/testing/risc64 example, in rust-async-broadcast/testing/riscv64 failures have logfiles that indicate that the actual tests don't even run, still it is being counted as a failure.
Also, looking at the description of "skip-not-installable":
This restrictions may cause a test to miss a regression due to
installability issues, so use with caution. If one only wants to
skip certain architectures, use the ``Architecture`` field for
that.
This test might have test dependencies that can't be fulfilled in
all suites or in derivatives. Therefore, when apt-get installs the
test dependencies, it will fail. Don't treat this as a test
failure, but instead treat it as if the test was skipped.