Fixes for release_3.2.0 #86

Job	Run time
Test Google C++ unittest (CPU Non-OMP)	6m 59s
Build 32-bit (i386)	1s
Configure variables for CI	1s
Test installing XGBoost lib + building the C API demo	5m 9s
Trigger Read The Docs build	0s
Build docs for the R package	-1s
Build docs for JVM packages	-1s
	12m 8s

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