package/fetchmail: bump version to 6.4.21

Release notes:
https://sourceforge.net/p/fetchmail/mailman/message/37333073/

"It contains the security fix for CVE-2021-36386 of 6.4.20, and fixes
a regression/a bug that causes log message truncation/run-together
prominently visible with --logfile that was introduced into 6.4.20."

Updated note for CVE-2021-36386:
https://sourceforge.net/p/fetchmail/mailman/message/37333078/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit b8a1d969b91b99ab2bf74ecb41402d21fee59b25)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/fetchmail/fetchmail.hash

@@ -1,6 +1,6 @@
 # From https://sourceforge.net/p/fetchmail/mailman/message/37327392/
-sha256  c82141ae2e8f0039ceb0c5c2eda43c5e93ad0bf7f9c6bb628092b3be74386176  fetchmail-6.4.20.tar.xz
+sha256  6a459c1cafd7a1daa5cd137140da60c18c84b5699cd8e7249a79c33342c99d1d  fetchmail-6.4.21.tar.xz
 # From https://sourceforge.net/projects/fetchmail/files/branch_6.4/
-sha1  ac6a6c4afa105e097d025340cf78b32e0c3b0c8e  fetchmail-6.4.20.tar.xz
+sha1  a264c50256c2b42d2c7893f9efae7c9a29350786  fetchmail-6.4.21.tar.xz
 # Locally computed:
 sha256  6346b5aa04e258fa4326272ea92372d796b4382aa963535ae98a3bb5f8cd5aeb  COPYING

package/fetchmail/fetchmail.mk

@@ -5,7 +5,7 @@
 ################################################################################
 
 FETCHMAIL_VERSION_MAJOR = 6.4
-FETCHMAIL_VERSION = $(FETCHMAIL_VERSION_MAJOR).20
+FETCHMAIL_VERSION = $(FETCHMAIL_VERSION_MAJOR).21
 FETCHMAIL_SOURCE = fetchmail-$(FETCHMAIL_VERSION).tar.xz
 FETCHMAIL_SITE = http://downloads.sourceforge.net/project/fetchmail/branch_$(FETCHMAIL_VERSION_MAJOR)
 FETCHMAIL_LICENSE = GPL-2.0; some exceptions are mentioned in COPYING