graphics/[lib]gphoto2: update to 2.5.26

LibCurl and LibXml2 now are mandatory to build driver for Lumix cameras

Changelog: http://www.gphoto.org/news/

No ABI change, no need to bump consumers

PR: 252959, 252960
Submitted by: fluffy
Approved by: maintainer (woodsb02)
MFH: 2021Q1