Update pytest requirement from <7,>=6 to >=6,<9

Updates the requirements on [pytest](https://github.com/pytest-dev/pytest) to permit the latest version.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/main/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@6.0.0...8.3.4)

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

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

pyproject.toml

@@ -78,7 +78,7 @@ optional-dependencies.release = [
 ]
 optional-dependencies.test = [
   "freezegun>=1,<2",
-  "pytest>=6,<7",
+  "pytest>=6,<9",
 ]
 urls.Homepage = "https://github.com/grafana-toolbox/grafanimate"
 urls.Issues = "https://github.com/grafana-toolbox/grafanimate/issues"