bump .ruby_version to jruby-9.4.8.0 (#16477)

jsvd · logstashmachine · commit f63231595706 · 2024-09-25T12:27:20.000Z
(cherry picked from commit 51cca73)
diff --git a/.ruby-version b/.ruby-version
@@ -1 +1 @@
-jruby-9.3.10.0
+jruby-9.4.8.0
