Test to cp/get/put directory with files with same name prefix

[john-jam]

One test case in gcsfs has a weird behavior where copying a folder also copy files that have the same name prefix as the folder name. For example:

# Files
# -- subdir.txt
# -- subdir
# ---- subfile.txt

fs.cp("subdir", "target")

# Expected target folder content: ["subfile.txt"]

# Content with gcsfs: ["subdir.txt", "subdir/subfile.txt"]

This PR adds tests to cover this use case.
Also, a PR in gcsfs adds a fix for this issue.

TODO:

• Update the target of this PR in gcsfs once this PR is merged.