BUILD couldn't be created in a directory which contains a directory called build

[eBeyond]

Describe the bug
If I run pants tailor :: I get this error:
`❯ pants tailor ::
10:17:24.86 [INFO] Initializing scheduler...
10:17:25.08 [INFO] Scheduler initialized.
10:17:25.28 [ERROR] 1 Exception encountered:

Engine traceback:
in tailor goal

IntrinsicError: Error opening file /client/BUILD for writing: Os { code: 21, kind: IsADirectory, message: "Is a directory" }
`
It's trying to create a BUILD File in there, but there is already an directory called 'build' in there. This directory cannot be renamed, because it's a generated one.

Pants version
2.20.0
OS
macOs

[huonw]

Ah, overlapping (case-insensitive) filenames is unfortunate. We could definitely improve the diagnostics here.

The default build_pattern option (https://www.pantsbuild.org/2.20/reference/global-options#build_patterns) includes any BUILD.* files, so a workaround would be to use file names like BUILD.pants. You can tell tailor what filename you want with https://www.pantsbuild.org/2.20/reference/goals/tailor#build_file_name e.g.

# pants.toml

...

[tailor]
build_file_name = "BUILD.pants"