fix for RFC/294 ; disallow enum <=> enum conversion

[timotheecour]

/cc @GULPF fix to unblock https://github.com/nim-lang/Nim/pull/16351 for accepted nim RFC https://github.com/nim-lang/RFCs/issues/294

(that's the only blocker for the PR)

CI failure unrelated IIUC, and should be fixed :)

[timotheecour]

after merging this, nimquery should be re-enabled in important_packages, see https://github.com/nim-lang/Nim/pull/16351

[timotheecour]

@GULPF CI failure seems unrelated

https://github.com/GULPF/nimquery/pull/10/checks?check_run_id=2124512704

Run jiro4989/setup-nim-action@v1.0.2
Error: Unable to process command '::set-env name=PATH,::/home/runner/.nimble/bin:/home/linuxbrew/.linuxbrew/bin:/home/linuxbrew/.linuxbrew/sbin:/opt/pipx_bin:/usr/share/rust/.cargo/bin:/usr/local/.ghcup/bin:/snap/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin' successfully.
Error: The `set-env` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands

[timotheecour]

PTAL, I added a commit that fixes CI (was broken prior to this PR, refs https://github.com/jiro4989/setup-nim-action/issues/42)

[timotheecour]

ping @GULPF

[timotheecour]

ping @GULPF