doc: Remove html comment in PULL_REQUEST_TEMPLATE #18380

This makes the dummy text visible so that it hopefully doesn't end up in merge commits, like here:

$ git log  --oneline --grep='<!--'
a421e0a22f Merge [#18376](/bitcoin-bitcoin/18376/): net: fix use-after-free in tests
dbb067da38 Merge [#18379](/bitcoin-bitcoin/18379/): doc: Comment fix merkle.cpp
712b7d9b47 Merge [#17804](/bitcoin-bitcoin/17804/): doc: Misc RPC help fixes
8625446b4d Merge [#17336](/bitcoin-bitcoin/17336/): scripts: search for first block file for linearize-data with some block files pruned
80fdb6fad1 Merge [#17442](/bitcoin-bitcoin/17442/): fix Typo: "merkelRoot" -> "merkleRoot"
224c19645f Merge [#17388](/bitcoin-bitcoin/17388/): Add missing newline in util_ChainMerge test
53f26cd11d Merge [#14421](/bitcoin-bitcoin/14421/): Fix path to doc/descriptors.md in 0.17 release notes
ea263e1eb0 Merge [#13243](/bitcoin-bitcoin/13243/): Make reusable base class for auxiliary indices
d3908e2cee Merge [#12759](/bitcoin-bitcoin/12759/): [Docs] Improve formatting of developer notes

Making it visible gives the pull request author a chance to see it and remove it. If it still ends up in the comment, it gives maintainers and editors a chance to see it and remove it.

ACK fad04f16d43968a401459ca1331a08affa60916a

As I was the one to introduce this comment in the first place in #16962 I'm divided about this, but okay, concept ACK, I definitely don't have the energy anymore to argue about anything. In any case an alternative would be to make the merge script strip out comments. (which might be preferable long-term in any case to avoid people putting "hidden" data in there)

(which might be preferable long-term in any case to avoid people putting "hidden" data in there) @laanwj I have opened pull requests for both suggestions. See here: https://github.com/bitcoin-core/bitcoin-maintainer-tools/pull/53

Personally I prefer to merge both changes, but merging just one of them should be good enough as well.

There's something to be said for that, especially if it makes people less lax in removing the message themselves saving the maintainers some trouble.

Though, if we do only the patch to the merge script it will automatically be detected if someone leaves the message in. If we do this and the patch to the merge script, this message will not be detected (it's up to the maintainer to see if someone left it in) but at least other 'hidden' comment data is rejected, which is good.

No strong opinion.

Not sure if this approach was previously discussed but how about adding some kind of unique string in the bottom of the template and then have a linter that detects it in the commit message? That would force people to take care of it themselves.

That sounds like an interesting approach (independent from this PR). Does Travis have access to the PR message? I guess a linter could query it through the github API with the same code as github-merge.py.

Github could allow us to see the raw comment in the UI. Maybe @DrahtBot could post it and warn the user to clean it? 🤷‍♂

Closing for now. I will reopen the next time this issue pops up again.