Depend on latest MCUboot stable release on master branch

There is no point in using MCUboot from main branch even on core
master. Core releases are depending on latest stable at point of
release so we move 'backward' anyway. It is better to test on
with what will likely be used for release.

repository.yml

@@ -126,7 +126,7 @@ repo.deps:
         repo: mcuboot
         branch: main
         vers:
-            master: 0-dev
+            master: 0-latest
             mynewt_1_7_0_tag: 1.3.1
             mynewt_1_8_0_tag: 1.5.0
             mynewt_1_9_0_tag: 1.7.2