Specify specific source for pulling homebrew container (carbon-language#2062)

- Since VS Code Dev container extention has a non-interactive shell, user
cannot select a specific image if there are multiple images under same
named authors.
- This fix ensures that images are only pulled from Docker Hub and no
interactive menu is presented.
- References: carbon-language#1816, carbon-language#1817
- Fixes carbon-language#2043

Signed-off-by: Avinal Kumar <[email protected]>

Author: avinal

.devcontainer/Dockerfile

@@ -3,7 +3,7 @@
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 ARG TAG=3.5.6
-FROM homebrew/brew:${TAG}
+FROM docker.io/homebrew/brew:${TAG}
 
 # Install libxcrypt using Homebrew.
 RUN brew install libxcrypt --overwrite