Fix GH-14888: README.REDIST.BINS refers to non-existing LICENSE [ci skip]

The LICENSE file of libmagic had been inadvertently removed when the
lib had been upgraded to 5.43. So we add t

Fix GH-14888: README.REDIST.BINS refers to non-existing LICENSE [ci skip]

The LICENSE file of libmagic had been inadvertently removed when the
lib had been upgraded to 5.43. So we add the file `COPYING` from that
release[1], and rename it to `LICENSE`.

[1] <https://github.com/file/file/releases/tag/FILE5_43>

Closes GH-14917.

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