docs: changelog entries for header value and rack.version fixes

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01F1KSHcsDNEP8o1k3QMwTFt

Author: chadlwilson

CHANGELOG.md

@@ -10,6 +10,9 @@
 - chore: revert `rack.version` value to be Rack 2.2 spec conformant
 - fix: handle Array response header values (Rack 3.x) for special-cased headers
 - fix: join repeated request header values instead of only passing the first
+- fix: do not mutate (potentially frozen) response header values when writing
+- fix: `rack.version` env value (Rack 2.x only) is now `Rack::VERSION` (the
+  protocol version Array the Rack 2 SPEC expects) instead of a release String
 
 Breaking API changes (for implementors of jruby-rack Java interfaces only)
 - `org.jruby.rack.RackEnvironment` gained a `getProtocol()` method (backing the