Update cibw config in pyproject.toml

Author: oscarbenjamin

pyproject.toml

@@ -85,7 +85,8 @@ package = "flint"
 build = "cp311-* cp312-* cp313-* cp313t-*" # pp311-*"
 skip = "*-win32 *-manylinux_i686 *-musllinux_*"
 
-free-threaded-support = true
+# Enable building for free-threaded CPython builds
+enable = ["cpython-freethreading"]
 
 manylinux-x86_64-image = "manylinux2014"
 manylinux-aarch64-image = "manylinux_2_28"