Added 42I64 - unsupported aggregation (#359)

Adds error for [PR](neo-technology/neo4j#31952)
- unsupported aggregation in NEXT.

Author: JoelBergstrand

modules/ROOT/content-nav.adoc

@@ -254,6 +254,7 @@
 **** xref:errors/gql-errors/42I60.adoc[]
 **** xref:errors/gql-errors/42I61.adoc[]
 **** xref:errors/gql-errors/42I62.adoc[]
+**** xref:errors/gql-errors/42I64.adoc[]
 **** xref:errors/gql-errors/42N00.adoc[]
 **** xref:errors/gql-errors/42N01.adoc[]
 **** xref:errors/gql-errors/42N02.adoc[]

modules/ROOT/pages/errors/gql-errors/42I64.adoc

@@ -0,0 +1,37 @@
+= 42I64
+
+== Status description
+error: syntax error or access rule violation - unsupported aggregation. { <<msg>> } currently not supported after `NEXT` { <<context>> }.
+
+== Example scenario
+
+For example, when aggregating in a `UNION` query after a `NEXT`:
+
+[source,cypher]
+----
+UNWIND [1, 2] AS x
+RETURN x
+
+NEXT
+
+RETURN COUNT(x)
+UNION ALL
+RETURN COUNT(x)
+----
+
+You will receive an error with GQLSTATUS xref:errors/gql-errors/42001.adoc[42001].
+This error has a cause detailed in xref:errors/gql-errors/42I64.adoc[42I64] and status description:
+
+
+[source]
+----
+error: syntax error or access rule violation - unsupported aggregation. Aggregations are currently not supported in `NEXT` when used in a `UNION`.
+----
+
+
+ifndef::backend-pdf[]
+[discrete.glossary]
+== Glossary
+
+include::partial$glossary.adoc[]
+endif::[]

modules/ROOT/pages/errors/gql-errors/index.adoc

@@ -1034,6 +1034,10 @@ Status description:: error: syntax error or access rule violation - missing LOOK
 
 Status description:: error: syntax error or access rule violation - unsupported distance metric. Unknown distance metric:  `{ <<input>> }`.
 
+=== xref:errors/gql-errors/42I64.adoc[42I64]
+
+Status description:: error: syntax error or access rule violation - unsupported aggregation. { <<msg>> } currently not supported in `NEXT` { <<context>> }.
+
 [role=label--changed-2025.03]
 === xref:errors/gql-errors/42N00.adoc[42N00]