git: Update to 2.26.1

Changes:
2.26.1
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This release is to address the security issue: CVE-2020-5260

* With a crafted URL that contains a newline in it, the credential
  helper machinery can be fooled to give credential information for
  a wrong host.  The attack has been made impossible by forbidding
  a newline character in any value passed via the credential
  protocol.

Credit for finding the vulnerability goes to Felix Wilhelm of Google
Project Zero.

(leot)