Long versions are sometimes problematic on Windows, because of MAX_PATH
issues. Versions for release builds don't contain the pre-release part, and
are thus usually short, but pre-release versions (which include an arbitrarily
long branch name) can get too long for Windows. This is a complication when
testing a release pipeline/process: we have to use final versioning just for
testing. This isn't ideal, so we special-case branch names that start with
`release-test/rt/`:
* Example: `iOS 15.1.123-rt` (and nothing else). This makes these versions
exactly 3 characters longer than the release version, which is hopefully
enough to avoid MAX_PATH issues on Windows.
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