Update dependency @antora/assembler to v1.0.0-beta.18 (#5415)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

package-lock.json

@@ -8,7 +8,7 @@
     "@antora/site-generator": "3.2.0-alpha.11"
   },
   "dependencies": {
-    "@antora/assembler": "1.0.0-beta.17",
+    "@antora/assembler": "1.0.0-beta.18",
     "@antora/collector-extension": "1.0.2",
     "@antora/lunr-extension": "1.0.0-alpha.13",
     "@antora/pdf-extension": "1.0.0-beta.18",