Upgrade to libheif v1.23.4 and libde265 v1.1.3

[github-actions]

Opened by the Check for libheif releases workflow.

• libheif: 1.23.3 → 1.23.4 (release notes)
• libde265: 1.1.2 → 1.1.3 (release notes)
• Emscripten: 3.1.60 → 3.1.61 (follows libheif's emscripten.yml)

The rebuilt src/lib and dist passed the smoke test in the run that opened this PR. Build libheif has been dispatched on this branch to check the committed files match a clean build; its result shows on the head commit.

Before merging, read the release notes for JS binding or build-emscripten.sh changes. After merging: bump the version, tag it, and update the dependency in Image Hopper.

[jakejackson1]

End-to-end test of the release check (opened from a throwaway branch pinned one release behind). All steps passed; closing and deleting the test branches.