Updated the OSU library URLs, which had the primary branch renamed
from "master" to "main", with a corresponding change to the name of
the tarball that gets downloaded by open_pdks.
diff --git a/sky130/Makefile.in b/sky130/Makefile.in
index 2bded28..55cdf4b 100644
--- a/sky130/Makefile.in
+++ b/sky130/Makefile.in
@@ -214,10 +214,10 @@
ALPHA_URL = https://github.com/PaulSchulz/sky130_pschulz_xx_hd/archive/master.tar.gz
XSCHEM_URL = https://github.com/StefanSchippers/xschem_sky130/archive/main.tar.gz
SRAM_URL = https://github.com/efabless/sky130_sram_macros/archive/main.tar.gz
-OSU_URL = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_osu_sc/+archive/refs/heads/master.tar.gz
-OSU_T12_URL = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_osu_sc_t12/+archive/refs/heads/master.tar.gz
-OSU_T15_URL = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_osu_sc_t15/+archive/refs/heads/master.tar.gz
-OSU_T18_URL = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_osu_sc_t18/+archive/refs/heads/master.tar.gz
+OSU_URL = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_osu_sc/+archive/refs/heads/main.tar.gz
+OSU_T12_URL = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_osu_sc_t12/+archive/refs/heads/main.tar.gz
+OSU_T15_URL = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_osu_sc_t15/+archive/refs/heads/main.tar.gz
+OSU_T18_URL = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_osu_sc_t18/+archive/refs/heads/main.tar.gz
# NOTE: Install destination is the git repository of the technology platform.
# Once updated in git, the git project can be distributed to all hosts.
