fetchmail: Update to 6.4.26

upstream changes:
-----------------
fetchmail-6.4.26 (released 2021-12-26, 31661 LoC):

# FIXES:
* When using wolfSSL 5.0.0, work around a bug that appears to hit wolfSSL when
  receiving handshake records while still in SSL_peek(). Workaround is to read
  1 byte and cache it, then call SSL_peek() again.
  This affects only some servers. https://github.com/wolfSSL/wolfssl/issues/4593

# TRANSLATIONS: language translations were updated by this fine person:
* sr:    Мирослав Николић (Miroslav Nikolić) [Serbian]

(triaxx)