mailmap: update Christian Brauner's email address

At least one of the addresses will stop functioning after February.
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

.mailmap

@@ -80,6 +80,9 @@ Chris Chiu <chris.chiu@canonical.com> <chiu@endlessos.org>
 Christian Borntraeger <borntraeger@linux.ibm.com> <borntraeger@de.ibm.com>
 Christian Borntraeger <borntraeger@linux.ibm.com> <cborntra@de.ibm.com>
 Christian Borntraeger <borntraeger@linux.ibm.com> <borntrae@de.ibm.com>
+Christian Brauner <brauner@kernel.org> <christian@brauner.io>
+Christian Brauner <brauner@kernel.org> <christian.brauner@canonical.com>
+Christian Brauner <brauner@kernel.org> <christian.brauner@ubuntu.com>
 Christophe Ricard <christophe.ricard@gmail.com>
 Christoph Hellwig <hch@lst.de>
 Colin Ian King <colin.king@intel.com> <colin.king@canonical.com>