parsePathFlakeRefWithFragment(): Handle 'path?query' without a fragment (backport #12157)

[mergify]

Motivation

Commands like nix flake metadata '.?submodules=1' ignored the query part of the URL, while nix build '.?submodules=1#foo' did work correctly because of the presence of the fragment part.

Before:

$ nix flake metadata '.?submodules=1'
Resolved URL:  git+file:///home/eelco/Dev/nix

After:

$ nix flake metadata '.?submodules=1'
Resolved URL:  git+file:///home/eelco/Dev/nix?submodules=1

Context

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This is an automatic backport of pull request #12157 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 28caa35 has failed:

On branch mergify/bp/2.25-maintenance/pr-12157
Your branch is up to date with 'origin/2.25-maintenance'.

You are currently cherry-picking commit 28caa35a9.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   tests/functional/flakes/flake-in-submodule.sh

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/libflake/flake/flakeref.cc

Cherry-pick of 83ff523 has failed:

On branch mergify/bp/2.25-maintenance/pr-12157
Your branch is ahead of 'origin/2.25-maintenance' by 1 commit.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 83ff52386.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/libflake/flake/flakeref.cc

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally