The subtree was moved from "shared/c-rbtree" to "src/c-rbtree". That confuses
git-subtree. To fix it, reimport the code with
rm -rf src/c-rbtree
git commit -a -m 'dummy commit'
git subtree add --prefix src/c-rbtree git@github.com:c-util/c-rbtree.git 8aa7bd1828eedb19960f9eef98d15543ec9f34eb --squash
Then rebase the result to drop the bogus dummy commit from the history.
To update the library use:
git subtree pull --prefix src/c-rbtree git@github.com:c-util/c-rbtree.git main --squash
