Drop Node.js 18.17 from GitLab and KAS images

We're using and testing Node.js 20 now. No need to build 18 anymore.

Part of https://gitlab.com/groups/gitlab-org/-/epics/13545

.gitlab/ci/gitlab.images.yml

@@ -38,6 +38,7 @@ gitlab:
     GRAPHICSMAGICK: '1.3.36'
     ARCH: linux/amd64,linux/arm64
     GIT: '2.36'
+    NODE: '20.12'
     RUST: '1.73'
   parallel:
     matrix:
@@ -46,7 +47,6 @@ gitlab:
         POSTGRESQL: ['13', '14', '15', '16']
         GOLANG: ['1.21', '1.22']
         CHROME: ['123']
-        NODE: ['18.17', '20.12']
 
 # Used by GitLab's compile-production-assets and compile-test-assets jobs
 gitlab-assets:
@@ -56,6 +56,7 @@ gitlab-assets:
   variables:
     RUBYGEMS: '3.4'
     LFS: '2.9'
+    NODE: '20.12'
     YARN: '1.22'
     GRAPHICSMAGICK: '1.3.36'
     ARCH: amd64,arm64
@@ -64,7 +65,6 @@ gitlab-assets:
       - OS: ['debian:bookworm']
         RUBY: ['3.0', '3.1', '3.2']
         GIT: ['2.33']
-        NODE: ['18.17', '20.12']
 
 # Used by GitLab's Review app jobs and triage-ops
 ep-native-cloud-services:

.gitlab/ci/kas.images.yml

@@ -19,8 +19,8 @@ gitlab-kas:
     YARN: '1.22'
     GRAPHICSMAGICK: '1.3.36'
     GIT: '2.36'
+    NODE: '20.12'
     POSTGRESQL: '12'
   parallel:
     matrix:
       - RUBY: ['3.0.patched', '3.1.patched', '3.2.patched']
-        NODE: ['18.17', '20.12']