graphics/libheif: Update to 1.17.6

Fixes following CVEs:
CVE-2023-49462
CVE-2023-49463

Changelog: https://github.com/strukturag/libheif/releases/tag/v1.17.6

References:
https://nvd.nist.gov/vuln/detail/CVE-2023-49462
https://nvd.nist.gov/vuln/detail/CVE-2023-49463

PR: 275873
Reviewed by: makc (maintainer)
Sponsored by: Blinkinblox