Support Building with Go 1.20

Robert Marshallrequested to merge
update-to-go-1-20 into master 
Support Building with Go 1.20

- Updates .tool-versions to 1.20.5
- Upstream alpine is already pinned to latest 1.20 series and needs no
  changes to work

Signed-off-by: Robert Marshall <rmarshall@gitlab.com>

This is a catch up to prepare for &10275 (closed) in %16.2

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