chore(github): dependabot changes

[qdm12]

Why this should be merged

Dependabot currently spams us with Go modules upgrades, which we need to handle manually/through a geth sync anyway. I believe the original idea was to have dependabot for github actions versions only.

How this works

• Do not monitor Go modules
• Ignore avalanchego Github action since it's meant to be updated at the same time as the Go module

How this was tested

Need to be documented?

Need to update RELEASES.md?

[qdm12]

~Actually we may want to disable dependabot, given it seems to bump commit hash of actions for every new commit on the default branch, I'll update this shortly.~

[maru-ava]

Maybe configure dependabot to only propose security updates as per the example of avalanchego?