Merge branch 'backport/jk/libcurl-8.7-regression-workaround' into maint-2.39

Fix was added to work around a regression in libcURL 8.7.0 (which has
already been fixed in their tip of the tree).

* jk/libcurl-8.7-regression-workaround:
  remote-curl: add Transfer-Encoding header only for older curl
  INSTALL: bump libcurl version to 7.21.3
  http: reset POSTFIELDSIZE when clearing curl handle

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>

diff --cc INSTALL
Simple merge

diff --cc http.c
Simple merge

diff --cc remote-curl.c
Simple merge