FindPkgConfig: Restore finding pkg-config before pkgconf
Since !6301 (merged), pkgconf is preferred over pkg-config
if they appear in the same directory. In some environments,
pkg-config may be a wrapper that adds semantics beyond either
pkgconf or the normal pkg-config. Prefer pkg-config over
pkgconf in order to preserve the prior behavior in such environments.
Fixes: #22976 (closed)
Backport: release