dependabot: update blinker requirement from ~=1.7 to ~=1.8

Updates the requirements on [blinker](https://github.com/pallets-eco/blinker) to permit the latest version.
- [Release notes](https://github.com/pallets-eco/blinker/releases)
- [Changelog](https://github.com/pallets-eco/blinker/blob/main/CHANGES.rst)
- [Commits](pallets-eco/blinker@1.7.0...1.8.1)

---
updated-dependencies:
- dependency-name: blinker
  dependency-type: direct:production
...

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

requirements_test.txt

@@ -1,4 +1,4 @@
 # Testing requirements
-blinker~=1.7
+blinker~=1.8
 pytest~=8.2.0
 pytest-mock~=3.14.0