meson.build: fix pkg-config generation

The code was previously using glib_dep.version() as a version for gio which
generates an invalid version like "gio-2.0 2.59.1" in the pkg-config file.
2 jobs for master in 3 minutes and 4 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #202492
build:ubuntu:autogen

00:03:04

passed #202493
build:ubuntu:meson

00:02:14