Fix some overlay algorithms output multipoint geometries but output layer is single point, causing insertion errors

[nyalldawson]

Fixes #49456

Needs tests

[agiudiceandrea]

@nyalldawson, since the bug is a regression introduced also in QGIS 3.22, shouldn't this PR be backported to the release-3_22 branch?

[nyalldawson]

@agiudiceandrea

Sorry, I didn't realise 3.22 was affected also

[qgis-bot]

The backport to queued_ltr_backports failed:

The process '/usr/bin/git' failed with exit code 1

stderr

error: could not apply 5fc7320fea... Fix some overlay algorithms output multipoint geometries but
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".

stdout

Auto-merging src/analysis/processing/qgsalgorithmdifference.cpp
CONFLICT (content): Merge conflict in src/analysis/processing/qgsalgorithmdifference.cpp
Auto-merging src/analysis/processing/qgsalgorithmfixgeometries.cpp
Auto-merging src/analysis/processing/qgsalgorithmsymmetricaldifference.cpp
CONFLICT (content): Merge conflict in src/analysis/processing/qgsalgorithmsymmetricaldifference.cpp
Auto-merging src/analysis/processing/qgsoverlayutils.cpp
CONFLICT (content): Merge conflict in src/analysis/processing/qgsoverlayutils.cpp
Auto-merging src/analysis/processing/qgsoverlayutils.h
CONFLICT (content): Merge conflict in src/analysis/processing/qgsoverlayutils.h

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-queued_ltr_backports queued_ltr_backports
# Navigate to the new working tree
cd .worktrees/backport-queued_ltr_backports
# Create a new branch
git switch --create backport-50567-to-queued_ltr_backports
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 5fc7320fea9c2f04d6dc5bdea0063218e33bce3f
# Push it to GitHub
git push --set-upstream origin backport-50567-to-queued_ltr_backports
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-queued_ltr_backports

Then, create a pull request where the base branch is queued_ltr_backports and the compare/head branch is backport-50567-to-queued_ltr_backports.