PyJWKClient: missing scheme allowlist enables CVE-2024-21643-class SSRF + token forgery via file://, ftp://, data: schemes

!NOTE The library does not directly return non-HTTPS URI contents to the attacker; the chained "plant a JWKS to forge tokens" scenario described in the original report requires additional application-layer flaws attacker write access to a filesystem path, untrusted jku derivation that this fix do...