NDK r25 beta 4 promoted to release candidate 1

[Dan Albert]

(resending an earlier message with a fixed subject)

NDK r25 beta 4 has been out for over a month and hasn't had any new bugs filed, so this build is now being promoted to release candidate 1. There is no new build to accompany this; beta 4 is RC 1.

If we do not receive any bug reports that meet the RC respin criteria (as described by https://github.com/android/ndk/wiki/NDK-Release-Process#lts-release-criteria), we'll ship NDK r25 to stable in about one month (no earlier than 14 July 2022).