ci: Cope with the fact that the "upstream" remote might already exist

Remove the old "upstream" remote if set, to make sure it points to the
right repo.
20 jobs for master in 7 minutes and 43 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Style
passed style-check #257479
debian amd64

00:00:22

 
  Build
passed build-debian #257480
debian amd64

00:00:40

passed build-debian-aarch64 #257488
aarch64 debian

00:01:25

passed build-debian-aarch64-clang-5 #257489
aarch64 debian

00:00:58

passed build-debian-armv7 #257492
armv7 debian

00:02:37

passed build-debian-armv7-clang-5 #257493
armv7 debian

00:01:08

passed build-debian-static #257481
debian amd64

00:00:35

passed build-debian-werror #257491
aarch64 debian

00:00:33

passed build-debian32 #257482
debian amd64

00:00:31

passed build-macos #257490
macos

00:00:30

passed build-win-arm32 #257486
debian amd64

00:00:31

passed build-win-arm64 #257487
debian amd64

00:00:30

passed build-win32 #257483
debian amd64

00:00:36

passed build-win32-unaligned-stack #257484
debian amd64

00:00:35

passed build-win64 #257485
debian amd64

00:00:41

 
  Test
passed test-debian #257494
debian amd64

00:00:45

passed test-debian-asan #257495
debian amd64

00:02:06

passed test-debian-msan #257496
debian amd64

00:01:02

passed test-debian-ubsan #257497
debian amd64

00:01:21

passed test-win64 #257498
debian amd64

00:00:52