`withLangVersionPreview` → `withLangVersion` in emitted IL tests when `LowerIntegralRangesToFastLoops` is out of preview

[brianrourkeboll]

Certain tests (6056c45, 6ed642e) needed to be run with langversion preview in #16650 to update their IL baselines. This should changed to the specific language version in these tests once the LowerIntegralRangesToFastLoops feature is out of preview — likely F# 9. (Ctrl + Shift + F for this issue number in the source.)

[vzarytovskii]

We don't want to remove them, but rather change them to using specific language (withLanguageVersion x.x), so we are sure we don't degrade any previous codegen/typechecking/etc.