<<<...Personally, I&#8217;m prepared to ignore it (it is very minor) but was just wondering what it was. >>>

Personally I would NOT iqnore it.  If the pipe continures to leak, it might split  and could destroy the engine due to overheating.

Check to make sure the clamps are tight, if they are and it still leaks- REPLACE it ASAP.

It is plastic and can fail, esp. after pipes have been removed during the headgasket replacement.

The cost is cheap @$26 (from my VW dealer in NC)
You might be able to reuse the coolant if it was all changed during the headgasket.

It seems to be a common part failure, along with the thermostat housings,that results from rebuilds or head gasket replacements.
The plastic seems to get briddle with age.  The good news is that the parts are cheap to replace.

I would also replace the thermostat housing at the same time.

Robert