ci: aks: switch from eastus2 to eastus region

This addresses an internal AKS issue that intermittently prevents
clusters from getting created. The fix has been rolled out to eastus but
not yet eastus2, so we unblock the CI by switching. No downsides in
general.

This supersedes #8990.

Fixes: #8989

Signed-off-by: Aurélien Bombo <abombo@microsoft.com>

tests/gha-run-k8s-common.sh

@@ -66,7 +66,7 @@ function create_cluster() {
     local rg="$(_print_rg_name ${test_type})"
 
     az group create \
-        -l eastus2 \
+        -l eastus \
         -n "${rg}"
 
     az aks create \