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.

Issue gh-19206

Signed-off-by: Josh Cummings <3627351+jzheaux@users.noreply.github.com>

docs/spring-security-docs.gradle

@@ -10,6 +10,10 @@ plugins {
 apply plugin: 'io.spring.convention.docs'
 apply plugin: 'java'
 
+node {
+	version = "24.15.0"
+}
+
 antora {
 	options = [clean: true, fetch: !project.gradle.startParameter.offline, stacktrace: true]
 	environment = [