Bump golang version to 1.20.13 and 1.21.6

[ahrtr]

What would you like to be added?

• Bump golang version to 1.20.13 for 3.5 and 3.4
• Bump golang version to 1.21.6 for main

Why is this needed?

To improve stability

[jmhbnz]

Completion tracking below:

• main dependency: upgrade go to 1.21.6 #17274
• release-3.5 (1.20.13) [3.5] dependency: upgrade go to 1.20.13 #17275
• release-3.4 (1.20.13) [3.4] dependency: update go to 1.20.13 #17276
• etcd-io CHANGELOG changelog: add 3.4 and 3.5 note about go 1.20.13 #17309
• etcd-io/bbolt main dependency: update go version to 1.21.6 bbolt#678
• etcd-io/raft main dependency: update go version to 1.21.6 raft#129

[ivanvc]

Can you assign this to me? Thanks

[ivanvc]

I'll update the CHANGELOG once #17274, #17275, and #17276 are merged.

[ahrtr]

All done. Thanks @ivanvc and @jmhbnz