Fix add and remove don

[AnieeG]

While calculating next DONID addDon cs was calling LatestCCIPDon.
If you remove the last don (n) LatestCCIPDon only gets n-1, and then sends expectedDonID as n but the expectedDonID in Capreg is not reclaimed as n for newly added don, it gets added with n+1 , therefore the addDon reverts with DonIdMismatch reason.
Replacing the LatestCCIPDon call with getNextDonId call from capreg to ensure it returns next available don id for adding a don.

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[cl-sonarqube-production]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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[github-actions]

Flakeguard Summary

Ran new or updated tests between develop and dc9ba39 (fix-remove-don).

View Flaky Detector Details | Compare Changes

Found Flaky Tests ❌

1 Results

Name	Pass Ratio	Panicked?	Timed Out?	Race?	Runs	Successes	Failures	Skips	Package	Package Panicked?	Avg Duration	Code Owners
TestUpdateTokenPriceFeedsFeeQuoterChangeset	0%	true	true	false	3	0	3	0	github.com/smartcontractkit/chainlink/deployment/ccip/changeset/v1_6	true	0s	@smartcontractkit/ccip-tooling, @smartcontractkit/ccip-offchain, @smartcontractkit/core, @smartcontractkit/deployment-automation

Artifacts

For detailed logs of the failed tests, please refer to the artifact failed-test-results-with-logs.json.

[kylesmartin]

Is the issue here that "nonce" has been taken and can't be used again? even if the DON corresponding to that nonce has been removed?

[AnieeG]

Is the issue here that "nonce" has been taken and can't be used again? even if the DON corresponding to that nonce has been removed?

Not sure it can be directly related to nonce , here is the removeDon ref which deletes the entry , next time when you next time try to add another DON it just increments the counter - it does not check whether the previous id is available because of the deletion