gcr: Fix LICENSE

The contents of the COPYING file included in the current source code
package match those of LGPL-2.0 license, which seems to have been the
case since 2011 commit
https://gitlab.gnome.org/GNOME/gcr/-/commit/c6691faa0348ab087e99ab9bd9914e1d5e81fa14



Signed-off-by: Niko Mauno <niko.mauno@vaisala.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>