fix(ci): upgrade pytest-cov/coverage for Python 3.14 annotation coverage

coverage.py < 7.6.10 incorrectly reports class annotations as uncovered
on Python 3.14 due to PEP 649 deferred evaluation (coveragepy#1908).
Pin pytest-cov >= 6.0.0 on Python >= 3.9 to pull coverage >= 7.6.10.

Author: fgmacedo

pyproject.toml

@@ -38,7 +38,8 @@ dev = [
     "pre-commit",
     "mypy",
     "pytest",
-    "pytest-cov",
+    "pytest-cov >=6.0.0; python_version >='3.9'",
+    "pytest-cov; python_version <'3.9'",
     "pytest-sugar >=1.0.0",
     "pytest-mock >=3.10.0",
     "pytest-benchmark >=4.0.0",