Fix flaky hardlinks test

[elboulangero]

The test was added in dc34990, it turns out that it's flaky. It failed once on the Debian build infra, cf. 1.

The problem is that the command rsync -aH '$fromdir/sym' '$todir' updates the mod time of $todir, so there might be a diff between the output of rsync_ls_lR $fromdir and rsync_ls_lR $todir, if ever rsync runs 1 second (or more) after the directories were created.

To clarify: it's easy to make the test fails 100% of the times with this change:

 makepath "$fromdir/sym" "$todir"
+sleep 5
 checkit "$RSYNC -aH '$fromdir/sym' '$todir'" "$fromdir" "$todir"

With the fix proposed here, we don't use checkit anymore, instead we just run the rsync command, then a simple diff to compare the two directories. This is exactly what the other -H test just above does.

In case there's some doubts, diff fails if sym is missing:

$ mkdir -p foo/sym bar
$ diff foo bar || echo KO!
Only in foo: sym
KO!

I tested that, after this commit, the test still catches the -H regression in rsync 3.4.0.

Fixes: #735

[Copilot]

Pull Request Overview

This PR fixes a flaky test in the hardlinks test suite that was causing intermittent failures on the Debian build infrastructure. The test was failing due to timing issues where rsync could update the modification time of the target directory, causing differences between source and destination when compared using rsync_ls_lR.

Key changes:

• Replace checkit function call with direct rsync command execution
• Add explicit diff comparison between source and destination directories
• Align the test approach with other hardlink tests in the same file

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