chore: Fix setting of isolated_flags in tests/test_find_package.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: jcfr

tests/test_find_package.py

@@ -94,7 +94,7 @@ def module(self, *args: str) -> None:
         return self.run(str(self.executable), "-m", *args)
 
     def install(self, *args: str, isolated: bool = True) -> None:
-        isolated_flags = "" if isolated else ["--no-build-isolation"]
+        isolated_flags = [] if isolated else ["--no-build-isolation"]
         self.module("pip", "install", *isolated_flags, *args)