Bump libwebp to v1.4.0

[vrabaud]

This is a follow-up on https://github.com/opencv/opencv/pull/25097

• [x] I agree to contribute to the project under Apache 2 License.
• [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• [x] The PR is proposed to the proper branch
• [x] There is a reference to the original bug report and related work