Git bash giving error of warning: unable to rmdir
warning: unable to rmdir on git checkout means that you're switching to a branch where this directory doesn't exist; git tries to remove it but there are some temporary files that git cannot remove; the directory is not empty so git cannot remove it also, hence the warning.
This happens mostly when your files are still in use. I personally experienced this sometimes with atom editor. Try to close your editor, and maybe any running compilers that are watching for changes too, and try to checkout again.
I know this is old, but in case anyone stumbles on this, as I did, it can also be that you're switching to a different branch and you have a Git submodule. Look for the .git hidden folder in the directory, you can delete it if you don't need it to be a submodule--just be sure to commit the folder to the parent repo in the current branch before switching.
rm -r .git