ci: pin go version to 1.20.5

[zhangzujian]

• Make sure you have followed Kube-OVN Code Style.

What type of this PR

• CI

Which issue(s) this PR fixes:

Fixes #(issue-number)

WHAT

🤖 Generated by Copilot at 7c24902

This pull request introduces a GO_VERSION environment variable to various GitHub workflows that use Go for building binaries and images for the kube-ovn project. This change improves the consistency and flexibility of the workflows and fixes some errors in the scheduled-e2e.yaml workflow.

🤖 Generated by Copilot at 7c24902

Sing, O Muse, of the valiant deeds of the kube-ovn team
Who, with skill and wisdom, updated their workflows with care
And made them consistent and flexible with the GO_VERSION variable
As the gods of GitHub watched and approved their noble efforts

HOW

🤖 Generated by Copilot at 7c24902

• Add GO_VERSION environment variable to specify the Go version for various workflows (link, link, link, link, link, link, link)
• Use GO_VERSION as an input to actions/setup-go@v2 action to set up the Go environment and allow for an empty value as a fallback option (link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link)
• Add missing steps to build the binaries and images for ovs, ovn, kube-ovn, and ovn4nfv in various workflows using make commands (link, link, link, link, link, link, link, link, link, link, link, link)