Update NodeJS to 24.15

This commit declares a NodeJS value whereas previously,
Antora would use the latest LTS version. When it updated to
Node 24.16, site production stopped, possibly due to
https://github.com/nodejs/node/commit/e95570c054.

Either way, it is helpful to have a pinned version in order
to stabilize builds, allowing us to update it in an orderly
fashion like other dependencies.

Closes gh-19206

build.gradle

@@ -3,6 +3,10 @@ plugins {
 	id 'org.antora' version '1.0.0'
 }
 
+node {
+	version = "24.15.0"
+}
+
 antora {
 	options = [clean: true, fetch: true, stacktrace: true]
 }