Fix failing readthedocs build #1323

Job	Run time
download_caravel	1m 40s
download_deps (pdk-with-volare)	2m 39s
download_deps (install_mcw)	3m 25s
download_deps (openlane)	54s
download_deps (setup-timing-scripts)	43s
download_deps (precheck)	1m 37s
RTL-verification (sky130A)	3m 49s
RTL-verification (sky130B)	4m 7s
hardening (sky130A)	55m 31s
hardening (sky130B)	1h 17m 59s
precheck (sky130A)	49m 58s
STA (sky130A)	8m 3s
precheck (sky130B)	37m 15s
	4h 7m 40s

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