github: do not allow FIXMEs in the changelog #6418

Job	Run time
config	8s
Download test chain database	3s
Build (9.6.4, 3.10, ubuntu-20.04, true)	2m 58s
Build (9.6.4, 3.10, ubuntu-22.04, true)	3m 51s
Slow tests (9.6.4, 3.10, ubuntu-20.04, true)	10m 1s
Benchmarks (9.6.4, 3.10, ubuntu-20.04, true)	9m 39s
Validate Devnet Database Snapshot and Replay Pact History (9.6.4, 3.10, ubuntu-20.04, true)	14s
Slow tests (9.6.4, 3.10, ubuntu-22.04, true)	10m 14s
Benchmarks (9.6.4, 3.10, ubuntu-22.04, true)	9m 40s
Build and publish docker image (9.6.4, ubuntu-20.04, true)	1m 4s
Validate Devnet Database Snapshot and Replay Pact History (9.6.4, 3.10, ubuntu-22.04, true)	17s
Unit tests (9.6.4, 3.10, ubuntu-20.04, true)	5m 1s
Publish (9.6.4, 3.10, ubuntu-20.04, true)	8s
Unit tests (9.6.4, 3.10, ubuntu-22.04, true)	5m 10s
Publish (9.6.4, 3.10, ubuntu-22.04, true)	7s
Run Integration Tests from remote repo	1m 4s
	59m 39s

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