Drop another Python 3.9 reference

Author: peterjc

.github/workflows/cibuildwheel.yml

@@ -16,7 +16,7 @@ jobs:
       # Install numpy with a wheel (do NOT compile it):
       CIBW_BEFORE_BUILD: "pip install --only-binary :all: -r requirements.txt"
       # There are/were no numpy wheels for these:
-      CIBW_SKIP: pp310-* cp39-manylinux_i686 cp310-manylinux_i686 cp311-manylinux_i686 cp312-manylinux_i686 *-musllinux_*
+      CIBW_SKIP: pp310-* cp310-manylinux_i686 cp311-manylinux_i686 cp312-manylinux_i686 *-musllinux_*
       # configure cibuildwheel to build native arch & aarch64 too
       CIBW_ARCHS_LINUX: auto aarch64
       # Quick test with C code using NumPy C API: