Bump gprd web workers from 24 to 28

Increase overall capacity.

See: https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/6087

environments/gprd/variables.tf

@@ -411,7 +411,7 @@ variable "node_count" {
     "stor"                  = 20
     "contributors"          = 1
     "multizone-stor"        = 9
-    "web"                   = 24
+    "web"                   = 28
     "web-pages"             = 8
     "web-cny"               = 2
     "api-cny"               = 2