Fix version crash when connecting to gotosocial

While gotosocial has a PR open to send a Mastodon-compatible version in
the `instance` endpoint, whatever it sends is unlikely to be helpful for
the purpose of version-gating features in the client library.

You can disable version-gating, but it still fails on instantiating
due to GtS's version not matching the semver regex. Fix this by moving
the version_check_mode above it, and not parsing the version if it's
turned off.

mastodon/Mastodon.py

@@ -421,20 +421,20 @@ class Mastodon:
                     if not (self.api_base_url is None or try_base_url == self.api_base_url):
                          raise MastodonIllegalArgumentError('Mismatch in base URLs between files and/or specified')
                     self.api_base_url = try_base_url
+
+        if not version_check_mode in ["created", "changed", "none"]:
+            raise MastodonIllegalArgumentError("Invalid version check method.")
+        self.version_check_mode = version_check_mode
         
         # Versioning
-        if mastodon_version == None:
+        if mastodon_version == None and self.version_check_mode != 'none':
             self.retrieve_mastodon_version()
-        else:
+        elif self.version_check_mode != 'none':
             try:
                 self.mastodon_major, self.mastodon_minor, self.mastodon_patch = parse_version_string(mastodon_version)
             except:
                 raise MastodonVersionError("Bad version specified")
         
-        if not version_check_mode in ["created", "changed", "none"]:
-            raise MastodonIllegalArgumentError("Invalid version check method.")
-        self.version_check_mode = version_check_mode
-        
         # Ratelimiting parameter check
         if ratelimit_method not in ["throw", "wait", "pace"]:
             raise MastodonIllegalArgumentError("Invalid ratelimit method.")