Subtheme script fails on Pantheon Integrated Composer Environment

Problem/Motivation

When using the script (./scripts/create_subtheme.sh ) to create a subtheme it fails.
On Pantheon using integrated composer.

cp: cannot stat '../contrib/bootstrap_barrio/subtheme': No such file or directory
./scripts/create_subtheme.sh: line 22: cd: name_bootstrap_barrio: No such file or directory
mv: cannot stat '*bootstrap_barrio_subtheme.*': No such file or directory
mv: cannot stat 'config/*/*bootstrap_barrio_subtheme.*': No such file or directory
mv: cannot stat '_name_bootstrap_barrio.theme': No such file or directory
sed: can't read : No such file or directory
sed: can't read name_bootstrap_barrio.info.yml: No such file or directory

Steps to reproduce

Install new D9 Integrated Composer site on Pantheon.
Install Bootstrap Barrio via composer.
Go to theme and run the script ./scripts/create_subtheme.sh

Proposed resolution

Pantheon uses the directory 'themes/composer' for all composer installed themes.

I think this should work if we changed lines 21-23:

cd ../../custom
cp -r ../composer/bootstrap_barrio/subtheme $CUSTOM_BARRIO
cd $CUSTOM_BARRIO

to

cp -r subtheme ../../custom/$CUSTOM_BARRIO
cd ../../custom/$CUSTOM_BARRIO

Remaining tasks

User interface changes

API changes

Data model changes