base/stable/12 - Rename stable/12 to 12.2-PRERELEASE

[T-Daemon]

From /base/stable/12, Revision 364897:

Date:     Fri Aug 28 00:00:37 2020 UTC (7 hours, 19 minutes ago)
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Rename stable/12 to 12.2-PRERELEASE, marking the start of the
12.2 release cycle.
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