CI: Check out latest skywater-pdk revision

.github/Makefile

diff --git a/.github/Makefile b/.github/Makefile
index fcb0bc1..0447bcf 100644
--- a/.github/Makefile
+++ b/.github/Makefile
@@ -17,7 +17,7 @@
 OPEN_PDKS_ROOT ?= $(shell pwd)/..
 THREADS ?= $(shell nproc)
 STD_CELL_LIBRARY ?= sky130_fd_sc_hd
-SKYWATER_COMMIT ?= b5ff6174d9aa921f670f12a2893969fe4a516f6c
+SKYWATER_COMMIT ?= main
 
 .DEFAULT_GOAL := all