webkitgtk,wpewebkit: Bump up version to 2.38.6

[psaavedra]

• wpewebkit's Release note: https://wpewebkit.org/release/wpewebkit-2.38.6.html
• webkitgtk's Release note: https://webkitgtk.org/2023/04/20/webkitgtk2.38.6-released.html