Update pip requirement from >=21.3.1 to >=26.1

Updates the requirements on [pip](https://github.com/pypa/pip) to permit the latest version.
- [Changelog](https://github.com/pypa/pip/blob/main/NEWS.rst)
- [Commits](pypa/pip@21.3.1...26.1)

---
updated-dependencies:
- dependency-name: pip
  dependency-version: '26.1'
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 colorlog==6.10.1
 homeassistant==2025.2.4
-pip>=21.3.1
+pip>=26.1
 ruff==0.14.14
 aionatgrid==0.4.0