Add class attribute protocol to HTTPFileSystem

[ap--]

Close #1934

Currently the protocol class attribute on the HTTPFileSystem depends on the first used http protocol, due to:

filesystem_spec/fsspec/registry.py

Lines 265 to 266 in 43e60fa

	if getattr(cls, "protocol", None) in ("abstract", None):
	cls.protocol = protocol

This PR adds a protocol classvar tuple to the filesystem class with http and https.

[martindurant]

Yes, this is the right fix.

For the test, I think a subprocess should be avoided - why can't the same code be run inside the session as normal?

[martindurant]

Note that the downstream error is new and unrelated.

[martindurant]

I simplified the test - this is equivalent?

[ap--]

Hi @martindurant, I used subprocess before to be able to create a failing test before the patch is applied. But your version is equivalent after the patch and ensures that the first (?default) protocol on the class will be 'http'. Thanks!