Bump pandas from 1.2.3 to 1.2.4 (AtsushiSakai#502)

Bumps [pandas](https://github.com/pandas-dev/pandas) from 1.2.3 to 1.2.4.
- [Release notes](https://github.com/pandas-dev/pandas/releases)
- [Changelog](https://github.com/pandas-dev/pandas/blob/master/RELEASE.md)
- [Commits](pandas-dev/pandas@v1.2.3...v1.2.4)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 numpy == 1.20.2
 scipy == 1.6.2
-pandas == 1.2.3
+pandas == 1.2.4
 matplotlib == 3.4.1
 cvxpy == 1.1.12