Update wp-cli.yml path after 43309

[JPry]

Now that [43309] has landed, the wp-cli.yml file should be updated to point to the build/ directory instead of the src/ directory.

[swissspidy]

#44220 was marked as a duplicate.

[danielbachhuber]

@johnbillion Why does this need to land in 4.9.7?

[pento]

In 43312:

Tools: Update wp-cli.yml to point to the build directory.

After [43309], WP-CLI should be running against the build directory, not the src directory.

Props jpry.
Fixes #44214.