gitk: allow Tcl/Tk 9.0+ for testing

Tcl/Tk 9.0 has been released, and is (to be) shipped in Fedora 42.
Allow gitk to (try to) run under this later package so that testing and
development can continue.

Signed-off-by: Mark Levedahl <[email protected]>

Author: mark987

gitk

@@ -7,7 +7,7 @@ exec wish "$0" -- "$@"
 # and distributed under the terms of the GNU General Public Licence,
 # either version 2, or (at your option) any later version.
 
-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 \