chore(CHANGELOG): set changes to the "Unreleased" section (would need…

… to merge back from `main` once 1.3.4 is released)

Also, fixes a broken link.

CHANGELOG.md

@@ -4,7 +4,7 @@ Changelog for the runtimes governed by the Polkadot Fellowship.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
-## [1.3.4] 01.11.2024
+## [Unreleased]
 
 ### Added
 
@@ -138,7 +138,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Fix claim queue size ([runtimes#381](https://github.com/polkadot-fellows/runtimes/pull/381), [SDK v1.14 #4691](https://github.com/paritytech/polkadot-sdk/pull/4691)).
 - `pallet-referenda`: Ensure to schedule referenda earliest at the next block ([runtimes#381](https://github.com/polkadot-fellows/runtimes/pull/381), [SDK v1.14 #4823](https://github.com/paritytech/polkadot-sdk/pull/4823)).
 - Don't partially modify HRMP pages ([runtimes#381](https://github.com/polkadot-fellows/runtimes/pull/381), [SDK v1.14 #4710](https://github.com/paritytech/polkadot-sdk/pull/4710)).
-- Coretime Chain: mitigate behaviour with many assignments on one core ([runtimes#434][https://github.com/polkadot-fellows/runtimes/pull/434]).
+- Coretime Chain: mitigate behaviour with many assignments on one core ([runtimes#434](https://github.com/polkadot-fellows/runtimes/pull/434)).
 - Port Agile Coretime migration from polkadot-sdk in order to fix leases with gaps handling([polkadot-fellows/runtimes#426](https://github.com/polkadot-fellows/runtimes/pull/426))
 
 #### From [#322](https://github.com/polkadot-fellows/runtimes/pull/322)