[ci] can launch compilation of manual even on non-release branches

.gitlab-ci.yml

@@ -99,8 +99,7 @@ check-opam-release:
 ################################################################################
 ### PRE-RELEASE
 
-make-manual:
-  <<: *when_release
+.build-template: &make_manual
   stage: prepare-release
   variables:
     OUT: "manual"
@@ -111,6 +110,14 @@ make-manual:
   script:
     - ./nix/ci.sh
 
+release-manual:
+  <<: *when_release
+  <<: *make_manual
+
+force-manual:
+  <<: *manual_template
+  <<: *make_manual
+
 check-versions:
   <<: *when_release
   stage: prepare-release