git-gui: Allow Tcl 9.0

TclTk 9.0 is now shipping, and git-gui is now patched to support use of
this newer version. Adjust required versions to allow Tcl/Tk >= 8.6,
including 9.x.

Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>

git-gui.sh

@@ -30,7 +30,7 @@ along with this program; if not, see <https://www.gnu.org/licenses/>.}]
 ##
 ## Tcl/Tk sanity check
 
-if {[catch {package require Tcl 8.6-8.8} err]} {
+if {[catch {package require Tcl 8.6-} err]} {
 	catch {wm withdraw .}
 	tk_messageBox \
 		-icon error \