20465 fix script re-upload

[arthanson]

Fixes: #20465

On re-upload deletes the old file so storage_save won't create a new filename.

[jeremystretch]

Rather than handling this manually, we should be able to leverage the allow_overwrite argument when invoking the ScriptFileSystemStorage backend. AFAICT this can be accomplished by adding an option under the DEFAULT_STORAGES setting:

DEFAULT_STORAGES = {
    "scripts": {
        "BACKEND": "extras.storage.ScriptFileSystemStorage",
        "OPTIONS": {
            "allow_overwrite": True,
        },
    },
}