[Makefile] update open_pdks commit to include the lef read fix

Makefile

diff --git a/Makefile b/Makefile
index 46ad6f9..5c3db80 100644
--- a/Makefile
+++ b/Makefile
@@ -14,7 +14,7 @@
 SPECIAL_VOLTAGE_LIBRARY ?= sky130_fd_sc_hvl
 IO_LIBRARY ?= sky130_fd_io
 SKYWATER_COMMIT ?= 3d7617a1acb92ea883539bcf22a632d6361a5de4
-OPEN_PDKS_COMMIT ?= 8688323e12530b9ced04b8053a6c4699b28402fc
+OPEN_PDKS_COMMIT ?= 3959de867a4acb6867df376dac495e33bb0734f1
 
 .DEFAULT_GOAL := ship
 # We need portable GDS_FILE pointers...