chore: update libheif to fix 100% CPU usage due to corrupted HEIC images

[skatsubo]

libheif v1.19.8 does not properly detect corrupted HEIC and spins in an infinite loop with full 1 core 100% CPU usage (per thread / thumbnail generation job).
Seems fixed in v1.20, see the main issue thread.

• main issue Thumbnails Not Generating After Uploading HEIC/DNG Photos immich#14349
• duplicate [BUG] The "Generate Thumbnails" job is stuck and it never finishes, and it permanently has a Immich process using up 100% of a CPU core (Each new job thread is another 100% CPU core). immich#20516
• libheif issue: Remove an invalid assertion that triggers fuzzers strukturag/libheif#1492

Another/unrelated noticeable change in v1.20:

You can specify a security limit for the maximum total memory libheif may use for decoding. This is easier to handle than specifying limits on the maximum image size or single memory allocations.