[SETUP][Thrive] Fix install_requires when setup thrive backend (#941)

Author: zhzhcookie

setup.py

@@ -984,7 +984,7 @@ def get_flagtree_version():
     long_description_content_type="text/markdown",
     install_requires=[
         "importlib-metadata; python_version < '3.10'",
-        "PyYAML>=6.0",
+        *(["PyYAML>=6.0"] if helper.flagtree_backend != "thrive" else []),
     ],
     packages=list(get_packages()),
     package_dir=dict(get_package_dirs()),