REGTESTS: Fix required versions for several scripts

The following scripts require HAProxy 2.4 :

 * cache/caching_rules.vtc
 * cache/post_on_entry.vtc
 * cache/vary.vtc
 * checks/1be_40srv_odd_health_checks.vtc
 * checks/40be_2srv_odd_health_checks.vtc
 * checks/4be_1srv_health_checks.vtc
 * converter/fix.vtc
 * converter/mqtt.vtc
 * http-messaging/protocol_upgrade.vtc
 * http-messaging/websocket.vtc
 * http-set-timeout/set_timeout.vtc
 * log/log_uri.vtc

However it may change is features are backported.
diff --git a/reg-tests/checks/1be_40srv_odd_health_checks.vtc b/reg-tests/checks/1be_40srv_odd_health_checks.vtc
index 7e8e431..bd07d88 100644
--- a/reg-tests/checks/1be_40srv_odd_health_checks.vtc
+++ b/reg-tests/checks/1be_40srv_odd_health_checks.vtc
@@ -6,7 +6,7 @@
 # The first health-checks passed tests are checked for all these servers
 # thanks to syslog messages.
 
-#REQUIRE_VERSION=1.8
+#REQUIRE_VERSION=2.4
 #EXCLUDE_TARGETS=freebsd
 #REGTEST_TYPE=slow
 
diff --git a/reg-tests/checks/40be_2srv_odd_health_checks.vtc b/reg-tests/checks/40be_2srv_odd_health_checks.vtc
index fb22959..d1cabbc 100644
--- a/reg-tests/checks/40be_2srv_odd_health_checks.vtc
+++ b/reg-tests/checks/40be_2srv_odd_health_checks.vtc
@@ -1,7 +1,7 @@
 varnishtest "Health-checks"
 feature ignore_unknown_macro
 
-#REQUIRE_VERSION=1.8
+#REQUIRE_VERSION=2.4
 #EXCLUDE_TARGETS=freebsd,osx,generic
 #REGTEST_TYPE=slow
 
diff --git a/reg-tests/checks/4be_1srv_health_checks.vtc b/reg-tests/checks/4be_1srv_health_checks.vtc
index b8bd105..2252490 100644
--- a/reg-tests/checks/4be_1srv_health_checks.vtc
+++ b/reg-tests/checks/4be_1srv_health_checks.vtc
@@ -1,7 +1,7 @@
 varnishtest "Health-check test"
 feature ignore_unknown_macro
 
-#REQUIRE_VERSION=1.8
+#REQUIRE_VERSION=2.4
 #EXCLUDE_TARGETS=freebsd
 #REGTEST_TYPE=slow