[3.14] Fix integer overflow for formats "s" and "p" in the struct module (GH-145750) (GH-145772)

(cherry picked from commit 4d0dce0c8ddc4d0321bd590a1a33990edc2e1b08)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>