Fix failing readthedocs build #1313

Job	Run time
download_caravel	2m 2s
download_deps (pdk-with-volare)	2m 59s
download_deps (install_mcw)	3m 55s
download_deps (openlane)	51s
download_deps (setup-timing-scripts)	42s
download_deps (precheck)	1m 50s
RTL-verification (sky130A)	5m 13s
RTL-verification (sky130B)	3m 49s
hardening (sky130A)	24m 45s
hardening (sky130B)	24m 44s
precheck	1s
STA	1s
	1h 10m 52s

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