go.mod: update net and protobuf packages for security review

[CaioTeixeira95]

What

Security review https://github.com/stellar/wallet-backend/security/dependabot/2 and https://github.com/stellar/wallet-backend/security/dependabot/1

Why

Solve security issues.

Known limitations

N/A

Checklist

PR Structure

• It is not possible to break this PR down into smaller PRs.
• This PR does not mix refactoring changes with feature changes.
• This PR's title starts with name of package that is most changed in the PR, or all if the changes are broad or impact many packages.

Thoroughness

• This PR adds tests for the new functionality or fixes.
• All updated queries have been tested (refer to this check if the data set returned by the updated query is expected to be same as the original one).

Release

• This is not a breaking change.
• This is ready to be tested in development.
• The new functionality is gated with a feature flag if this is not ready for production.

[marcelosalloum]

LGTM!