workflows: use symbolic name in go-version

[phlogistonjohn]

Depends on: #313
Depends on: #288

The workflow files that use Go directly (as opposed to inside a container) use actions/setup-go - this action gained an ability to use "relative versions" of stable and oldstable in the last year or two.

Switch our workflow file to use oldstable rather than a specific version number in order to keep up with releases from Go upstream. Use oldstable as to ensure the older but still actively maintained version of Go works.

This doesn't handle the container image... that's a WIP project for another PR.

[dpulls]

🎉 All dependencies have been resolved !

[mergify]

This pull request now has conflicts with the target branch. Please resolve these conflicts and force push the updated branch.

[obnoxxx]

@Mergifyio rebase

[mergify]

rebase

❌ Base branch update has failed

Git reported the following error:

warning: skipped previously applied commit be235b3
warning: skipped previously applied commit 4dc447b
warning: skipped previously applied commit 4c945b9
hint: use --reapply-cherry-picks to include skipped commits
hint: Disable this message with "git config advice.skippedCherryPicks false"
Rebasing (1/2)
The previous cherry-pick is now empty, possibly due to conflict resolution.
If you wish to commit it anyway, use:

    git commit --allow-empty

Otherwise, please use 'git rebase --skip'
interactive rebase in progress; onto d28e94b
Last command done (1 command done):
   pick d3e0266 build: Bump Go version to 1.19
Next command to do (1 remaining command):
   pick 7c39826 workflows: use symbolic name oldstable instead of a particular version
  (use "git rebase --edit-todo" to view and edit)
You are currently rebasing branch 'jjm-go-vers' on 'd28e94b'.
  (all conflicts fixed: run "git rebase --continue")

nothing to commit, working tree clean
Could not apply d3e0266... build: Bump Go version to 1.19

err-code: 06DC6

[dpulls]

🎉 All dependencies have been resolved !

[synarete]

LGTM

[anoopcs9]

That's cool.