luci: speculatively upgrade xcode sdk and tool version for Mac
luci: speculatively upgrade xcode sdk and tool version for Mac

Hopefully will fix XCode failures on LUCI bots.

Change-Id: Icd76ddc938ea77a2faecbf347411adc0c9144d4d
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto