Merge branch 'jk/http-test-fixes'

Various fix-ups on HTTP tests.

* jk/http-test-fixes:
  t5559: make SSL/TLS the default
  t5559: fix test failures with LIB_HTTPD_SSL
  t/lib-httpd: enable HTTP/2 "h2" protocol, not just h2c
  t/lib-httpd: respect $HTTPD_PROTO in expect_askpass()
  t5551: drop curl trace lines without headers
  t5551: handle v2 protocol in cookie test
  t5551: simplify expected cookie file
  t5551: handle v2 protocol in upload-pack service test
  t5551: handle v2 protocol when checking curl trace
  t5551: stop forcing clone to run with v0 protocol
  t5551: handle HTTP/2 when checking curl trace
  t5551: lower-case headers in expected curl trace
  t5551: drop redundant grep for Accept-Language
  t5541: simplify and move "no empty path components" test
  t5541: stop marking "used receive-pack service" test as v0 only
  t5541: run "used receive-pack service" test earlier

This is a backport onto the `maint-2.39` branch, starting to take care
of making that branch's CI builds healthy again.

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