FindPython: fix handling when FIND_VIRTUALENV == FIRST

Fixes: #20525
diff --git a/Modules/FindPython/Support.cmake b/Modules/FindPython/Support.cmake
index 67db4d3..50dd7ba 100644
--- a/Modules/FindPython/Support.cmake
+++ b/Modules/FindPython/Support.cmake
@@ -953,7 +953,7 @@
           if (_${_PYTHON_PREFIX}_EXECUTABLE)
             break()
           endif()
-          if (NOT _${_PYTHON_PREFIX}_FIND_VIRTUALENV STREQUAL "ONLY")
+          if (_${_PYTHON_PREFIX}_FIND_VIRTUALENV STREQUAL "ONLY")
             break()
           endif()
         endif()