package/libcurl: bump to version 7.64.1

Contains a number of fixes for issues discovered post-7.64.0.  For details,
see the list of changes:

https://curl.haxx.se/changes.html#7_64_1



Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>