Gardening: fix typo in swift_build_support product.py

Author: MaxDesiatov

utils/swift_build_support/swift_build_support/products/product.py

@@ -61,7 +61,7 @@ def is_build_script_impl_product(cls):
     def is_swiftpm_unified_build_product(cls):
         """is_swiftpm_unified_build_product -> bool
 
-        Whether this product should be build in the unified build of SwiftPM
+        Whether this product should be built in the unified build of SwiftPM
         products.
         """
         return False