chore(ci): run on both stable and oldstable

Author: tmzane

.github/workflows/checks.yml

@@ -10,8 +10,6 @@ on:
 jobs:
   test:
     uses: go-simpler/.github/.github/workflows/test.yml@main
-    with:
-      go-versions: '[ "stable" ]' # current "oldstable" (1.20) does not contain the "slices" package.
   lint:
     uses: go-simpler/.github/.github/workflows/lint.yml@main
   vuln: