chore: Set Mainnet upgrade epoch for NV23

[rjan90]

Proposed Changes

• Sets the Mainnet upgrade epoch for NV23 to epoch 4154640 corresponding to 2024-08-07T12:00:00Z in the master branch.

Additional Info

Due to #12112, which moved build/params_mainnet.go to build/buildconstants/params_mainnet.go in the master-branch I can´t land this in master and then backport to #12271 which is the preferred way. I have therefore set the upgrade epoch in the coming v1.28.0 stable release prep PR in this commit: 2cb46a9 as well.

Checklist

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