bug: unstrip_protocol incorrectly returns original path

[jonburdo]

In version 2022.5.0, AbstractFileSystem.unstrip_protocol fails to preprend protocol:// to the path if the path happens to start with the characters of one of the class's protocols. For example:

from fsspec.spec import AbstractFileSystem

AbstractFileSystem().unstrip_protocol('abstract-file')
# 'abstract-file'

from s3fs import S3FileSystem

S3FileSystem().unstrip_protocol('s3-file')
# 's3-file'

S3FileSystem().unstrip_protocol('s3a-file')
# 's3a-file'

It works correctly any time the beginning of the path does not match the protocol:

AbstractFileSystem().unstrip_protocol('aabstract-file')
# 'abstract://aabstract-file'

S3FileSystem().unstrip_protocol('ss3-file')
# 's3://ss3-file'

Instead of returning the original path any time it starts with one of the protocols, the function should instead check for protocol + "://".