graphics/osgearth: Fix build with protobuf 22+

Note that this port has a PLIST issue if libzip is installed.

> Checking for pkg-plist issues (check-plist)

> Parsing plist

> Checking for items in STAGEDIR missing from pkg-plist

Error: Orphaned: lib/osgPlugins-3.6.5/osgdb_zip.so

> Checking for items in pkg-plist which are not in STAGEDIR

> Error: Plist issues found.

• Error code 1