Revert to Go 1.18 in go.mod and make policy around this official #390

The pull request embarked with main (dff3a92) will be merged soon

Required conditions for merge:

#approved-reviews-by>=1 [🛡 GitHub branch protection]
- #390
#changes-requested-reviews-by=0 [🛡 GitHub branch protection]
- #390
check-success=lint
check-success=test
all of [📃 From pull request rule Automatic merge on approval]:
- #approved-reviews-by>=1
  - #390
- #changes-requested-reviews-by=0
  - #390
- -draft [📌 queue requirement]
  - #390
- base=main
- check-success='lint'
- check-success='test'
- label!=do-not-merge
  - #390
- label=ready-to-merge
  - #390
- any of [📌 queue -> configuration change requirements]:
  - -mergify-configuration-changed
    - #390
  - check-success=Configuration changed
- any of [🔀 queue conditions]:
  - all of [📌 queue conditions of queue default]:
    - #approved-reviews-by>=1 [🛡 GitHub branch protection]
      - #390
    - #changes-requested-reviews-by=0 [🛡 GitHub branch protection]
      - #390
    - any of [🛡 GitHub branch protection]:
      - check-success=lint
      - check-neutral=lint
      - check-skipped=lint
    - any of [🛡 GitHub branch protection]:
      - check-success=test
      - check-neutral=test
      - check-skipped=test
any of [🛡 GitHub branch protection]:
- check-success=lint
- check-neutral=lint
- check-skipped=lint
any of [🛡 GitHub branch protection]:
- check-success=test
- check-neutral=test
- check-skipped=test

Check-runs and statuses of the embarked pull request #390:

		lint	details
		test	details