Merge pull request #2311 from The-OpenROAD-Project-staging/sky130hd-gcd-tighten

sky130hd/gcd: tighten due to 0 tns

Author: maliberty

flow/designs/sky130hd/gcd/constraint.sdc

@@ -2,7 +2,7 @@ current_design gcd
 
 set clk_name  core_clock
 set clk_port_name clk
-set clk_period 3.4
+set clk_period 2.5
 set clk_io_pct 0.2
 
 set clk_port [get_ports $clk_port_name]