CI: vtest: Rely on VTest2 to run regression tests

VTest2 (https://github.com/vtest/VTest2) was released and is a remplacement
for VTest. VTest was archived. So let's use the new version now.

If this commit is backported, the 2 following commits must also be
backported:

 * 2808e3577 ("REGTESTS: Explicitly allow failing shell commands in some scripts")
 * 82c291124 ("REGTESTS: Make the script testing conditional set-var compatible with Vtest2")

reg-tests/README

@@ -14,7 +14,7 @@ See also: doc/regression-testing.txt
 
 * vtest compilation *
 
-    $ git clone https://github.com/vtest/VTest
+    $ git clone https://github.com/vtest/VTest2
 
     $ cd VTest
 

scripts/build-vtest.sh

@@ -2,7 +2,7 @@
 
 set -eux
 
-curl -fsSL https://github.com/wlallemand/VTest/archive/refs/heads/haproxy-sd_notify.tar.gz -o VTest.tar.gz
+curl -fsSL https://github.com/vtest/VTest2/archive/main.tar.gz  -o VTest.tar.gz
 mkdir ../vtest
 tar xvf VTest.tar.gz -C ../vtest --strip-components=1
 # Special flags due to: https://github.com/vtest/VTest/issues/12