Auto merge of #130072 - ChrisDenton:split-ci, r=Kobzol

Split x86_64-msvc-ext into two jobs

This is an attempt to mitigate (but not resolve) the high failure rate of the x86_64-msvc-ext builder. The theory being that doing less makes it less likely to fail. But this may not work as having an extra job that may fail might be worse.

try-job: x86_64-msvc-ext
try-job: x86_64-msvc-ext2

Author: bors