Fix issue 21302: std.uni's documentation contains a dead link to its …

[ghost]

…source file

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21302	trivial	std.uni's documentation contains a dead link to its source file

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#7658"