Update CHANGELOG: Fix handling of duplicate terms in SparsePolynomial #3126

Job	Run time
List directories for parallelizing tests	2s
Check no_std	22s
Check (stable)	1m 8s
Check (nightly)	1m 3s
Check Documentation	58s
Check Style	12s
Test (stable)	9m 17s
Test (nightly)	17m 27s
Test assembly	8m 20s
Test (cp6_782/)	28m 53s
Test (mnt4_753/)	12m 40s
Test (mnt6_753/)	25m 5s
Test (./pallas)	1m 16s
Test (./ed25519)	57s
Test (./ed_on_mnt4_753)	3m 46s
Test (./bn254)	2m 20s
Test (./bls12_381)	3m 17s
Test (./secp384r1)	1m 22s
Test (./bw6_767)	4m 1s
Test (./grumpkin)	1m 8s
Test (./curve25519)	1m 5s
Test (./ed_on_bls12_377)	1m 8s
Test (./ed_on_mnt4_298)	1m 13s
Test (./vesta)	1m 5s
Test (./ed_on_bls12_381_bandersnatch)	1m 15s
Test (./bls12_377)	4m 8s
Test (./ed_on_bw6_761)	36s
Test (./mnt4_298)	3m 47s
Test (./secp256k1)	1m 2s
Test (./ed_on_bn254)	1m 1s
Test (./ed_on_bls12_381)	1m 21s
Test (./secp256r1)	58s
Test (./bw6_761)	4m 2s
Test (./secq256k1)	58s
Test (./mnt6_298)	5m 33s
Test (./ed_on_cp6_782)	1m 16s
	2h 34m 2s

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