Fix boring tap of non-passive source from parent.

[dtzSiFive]

Expected result is fully aligned, which is what happens when reading from a probe.

When the source is already at the LCA (from parent) there's no probe and the secret connections only support a few commands.

For lack of a way to do, e.g., :#= here,
use read(probe(x)) to get the fully aligned result that's expected and bored down to the child.

This isn't ideal but fixes this using only the sorts of expressions and commands that we've already committed to supporting.

Fixes #3557.

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Type of Improvement

• Bugfix

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Release Notes

Fix tapping mix-alignment signal from parent.

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