downgraded pytest cov for python 3.7 support

pyproject.toml

@@ -23,6 +23,6 @@ classifiers=[
 [project.optional-dependencies]
 testing = [
     "pytest>=8.0",
-    "pytest-cov>=6.0",
+    "pytest-cov>=5,<6",  # Use pytest-cov version 5.x which supports Python 3.8
     "requests>=2.0"
 ]
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