Fix node version to 16

Temporary workaround for:

Error message "error:0308010C:digital envelope routines::unsupported"

See e.g. discussion at https://stackoverflow.com/questions/69692842/error-message-error0308010cdigital-envelope-routinesunsupported

This is intended to solve the immediate problem of a broken build; when we are back up and running, I'll ticket an upgrade to more recent node.

.gitlab-ci.yml

@@ -7,6 +7,8 @@ build-esap-gui:
     image: node:lts
     before_script:
       - 'command -v ssh-agent >/dev/null || ( apt-get update -y && apt-get install openssh-client -y )'
+    variables:
+      NODE_OPTIONS: "--openssl-legacy-provider"
     script:
       - node -v
       - npm -version
@@ -19,8 +21,6 @@ build-esap-gui:
         expire_in: 1 hour
         paths:
             - build
-    only:
-        - master
 
 deploy-esap-gui:
     stage: deploy