These files are already BSD-3-Clause even without the headers, but
adding these comments and the `LICENSE-BSD` symlink to the root level
`LICENSE` file are helpful to reinforce that there are only two
particular files in the `fuzzing/` that are not under BSD-3-Clause.

See:
gitpython-developers#1901 (comment)

While discussing adding similar license comments to the shell scripts
introduced in PR gitpython-developers#1901, it was noticed that the shell scripts in the
repository root directory did not have such comments and suggested that
we could add them when the scripts in the `fuzzing/` directory were
updated, so this commit does just that.

See:
gitpython-developers#1901 (comment)