Fix placement of perimeter labels with HTML formatting enabled

[nyalldawson]

Fixes #51829

[qgis-bot]

The backport to release-3_28 failed:

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

stderr

error: could not apply 21997c2ef8... Add test
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/core/labeling/qgsvectorlayerlabelprovider.cpp
[backport-51840-to-release-3_28 c2294662c7] Fix placement of perimeter labels with HTML formatting enabled
 Author: Nyall Dawson <nyall.dawson@gmail.com>
 Date: Tue Feb 14 09:10:24 2023 +1000
 1 file changed, 1 insertion(+), 1 deletion(-)
Auto-merging src/analysis/processing/qgsalgorithmextractlabels.cpp
Auto-merging src/core/labeling/qgspallabeling.cpp
Auto-merging src/core/labeling/qgsvectorlayerlabelprovider.cpp
[backport-51840-to-release-3_28 ffc6748d74] Use switches for curved label placement detection in more places to hopefully avoid future issues if more curved placement modes are introduced
 Author: Nyall Dawson <nyall.dawson@gmail.com>
 Date: Tue Feb 14 09:22:13 2023 +1000
 4 files changed, 135 insertions(+), 44 deletions(-)
Auto-merging tests/src/core/testqgslabelingengine.cpp
CONFLICT (content): Merge conflict in tests/src/core/testqgslabelingengine.cpp

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-release-3_28 release-3_28
# Navigate to the new working tree
cd .worktrees/backport-release-3_28
# Create a new branch
git switch --create backport-51840-to-release-3_28
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 2259924db64aca92fa5b6203cff17bb2c6de5a05,7f031b1e7c23b8aef34e4fc7c3383d6899b002ba,21997c2ef800ca060373bc2c7bd6833c4ec684bb
# Push it to GitHub
git push --set-upstream origin backport-51840-to-release-3_28
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release-3_28

Then, create a pull request where the base branch is release-3_28 and the compare/head branch is backport-51840-to-release-3_28.