[ENH] Fix sort by appearance bug when dropna=True (#1169)

* fix sort_by_appearance bug in the presence of dropna=True

* use sort_index for sort_by_appearance

* update type hints

* Use np.argsort instead of sort_index

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* dropna and sort_by_appearance test added

* add Issue/PR ref to test

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: samukweku

CHANGELOG.md

@@ -24,6 +24,7 @@
 -   [INF] Cancel old workflow runs via Github Action `concurrency`. PR #1161 @Zeroto521
 -   [ENH] Faster computation for non-equi join, with a numba engine. Issue #1102 @samukweku
 -   [BUG] Avoid `change_type` mutating original `DataFrame`. PR #1162 @Zeroto521
+-   [ENH] Fix error when `sort_by_appearance=True` is combined with `dropna=True`. Issue #1168 @samukweku
 
 ## [v0.23.1] - 2022-05-03