dont dockerignore .yarn (#27063)

.yarn is checked in and should be copied over to access the yarn
executable

Co-authored-by: Neil Fulwiler <[email protected]>

Author: neilfulwiler

.dockerignore

@@ -1,6 +1,5 @@
 .git/
 **/.tox/
-**/.yarn/
 **/__pycache__/
 **/*.egg-info/
 **/node_modules/