Add signature_methods=IMPLICIT for ppirc and gimp.org servers

fix #3351

See https://github.com/randombit/botan/issues/1558
20 jobs for master in 12 minutes and 59 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #14543
docker
build:1

00:02:24

22.7%
passed #14544
docker
build:2

00:02:24

22.6%
passed #14545
docker
build:3

00:02:29

22.9%
passed #14546
docker
build:4

00:02:00

17.3%
passed #14547
docker
build:5

00:02:27

23.0%
passed #14548
docker
build:6

00:02:12

23.1%
passed #14541
docker
build:alpine

00:02:00

manual #14542
armv7l allowed to fail manual
build:archlinux
passed #14540
docker
build:debian

00:02:42

29.8%
passed #14539
docker
build:fedora

00:02:25

22.2%
passed #14549
docker
build:without_udns

00:02:21

22.6%
 
  Test
passed #14553
docker
test:alpine

00:03:33

passed #14550
docker
test:debian

00:03:28

65.0%
passed #14551
docker
test:fedora

00:03:14

85.7%
passed #14554
freebsd
test:freebsd

00:03:39

passed #14552
docker
test:without_udns

00:03:14

85.7%
 
  Packaging
passed #14557
docker allowed to fail
packaging:archlinux

00:04:23

passed #14556
docker allowed to fail
packaging:deb

00:04:02

passed #14555
docker allowed to fail
packaging:rpm

00:01:15

 
  External
manual #14558
docker allowed to fail manual
coverity