Fix Issue 20539 - std.conv.to: internal overload conflict for enums with base types that have a catch-all opEquals overload (?)

[berni44]

This is a copy of #7378. I'm the original author, but as I deleted my old account, I can't do any changes there.

I rebased and replaced "issue 20539" by a link to bugzilla.

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20539	minor	std.conv.to: internal overload conflict for enums with base types that have a catch-all opEquals overload (?)

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + phobos#7749"

[RazvanN7]

Thanks for this! Just fix the nit below.