Update Yarn to v4.12.0 (#1075)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: Elizabeth Craig <elcraig@microsoft.com>

Author: renovate[bot]

.gitignore

@@ -7,7 +7,7 @@ node_modules/
 lib/
 package-lock.json
 # ignore when switching between yarn 1/4 branches
-.yarn
+/.yarn
 
 docs/.vuepress/.cache
 docs/.vuepress/.temp