Update pipdeptree requirement from ~=2.23 to ~=2.26

Updates the requirements on [pipdeptree](https://github.com/tox-dev/pipdeptree) to permit the latest version.
- [Release notes](https://github.com/tox-dev/pipdeptree/releases)
- [Commits](tox-dev/pipdeptree@2.23.0...2.26.1)

---
updated-dependencies:
- dependency-name: pipdeptree
  dependency-version: 2.26.1
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements-dev.txt

@@ -13,7 +13,7 @@ unittest-xml-reporting~=3.2
 testbook~=0.4
 
 # analyze dependencies
-pipdeptree~=2.23
+pipdeptree~=2.26
 
 # uploading to pypi
 build~=1.2