chore: bump Go to 1.20

[DmitriyLewen]

Description

Bump Go to 1.20

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Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[DmitriyLewen]

Now we can't install different modules with different versions with the same command:

root@c5244beadb12:/go# go install \
    github.com/twitchtv/twirp/protoc-gen-twirp@v8.1.0 \
    google.golang.org/protobuf/cmd/protoc-gen-go@v1.27.1 \
    github.com/magefile/mage@v1.14.0
go: google.golang.org/protobuf/cmd/protoc-gen-go@v1.27.1: all arguments must refer to packages in the same module at the same version (@v8.1.0)
root@c5244beadb12:/go# go install     github.com/twitchtv/twirp/protoc-gen-twirp@v8.1.0     google.golang.org/protobuf/cmd/protoc-gen-go@v1.27.1     github.com/magefile/mage@v1.14.0
go: google.golang.org/protobuf/cmd/protoc-gen-go@v1.27.1: all arguments must refer to packages in the same module at the same version (@v8.1.0)