Devenv: fix permission failures for mysql_tests and postgres_tests docker blocks (#44203)

devenv/docker/blocks/mysql_tests/Dockerfile

@@ -1,4 +1,5 @@
 ARG mysql_version=5.6
 FROM mysql:${mysql_version}
 ADD setup.sql /docker-entrypoint-initdb.d
+RUN chown -R mysql:mysql /docker-entrypoint-initdb.d/
 CMD ["mysqld"]

devenv/docker/blocks/postgres_tests/Dockerfile

@@ -1,4 +1,5 @@
 ARG postgres_version=9.3
 FROM postgres:${postgres_version}
 ADD setup.sql /docker-entrypoint-initdb.d
+RUN chown -R postgres:postgres /docker-entrypoint-initdb.d/
 CMD ["postgres"]