CI: validate jobs also check stdlib

validate-template is implemented such that we don't need to modify it,
we just add dependencies.

.gitlab-ci.yml

@@ -163,7 +163,7 @@ before_script:
 
 # set "needs" when using
 .validate-template:
-  stage: build-1
+  stage: build-2
   interruptible: true
   extends: .auto-use-tags
   needs:
@@ -577,8 +577,10 @@ validate:base:
   extends: .validate-template
   needs:
     - build:base
+    - library:ci-stdlib
   only: *full-ci
 
+# we currently don't have a stdlib+32bit job
 validate:base+32bit:
   extends: .validate-template
   needs:
@@ -592,6 +594,7 @@ validate:edge+flambda:
   image: $EDGE_IMAGE
   needs:
     - build:edge+flambda
+    - library:ci-stdlib+flambda
   variables:
     OPAM_VARIANT: "+flambda"
   only: *full-ci