Fix syntax error in `.readthedocs.yaml` #1089

Job	Run time
macosx-build	2m 25s
standard-build (--enable-debug --enable-cuckoo --enable-magic --enable-macho --enable-pb-tests --...	3m 32s
bazel-build	1m 19s
standard-build (--enable-debug --enable-profiling --enable-cuckoo --enable-magic --enable-macho -...	3m 29s
bigendian	11m 33s
mingw-build (--host=x86_64-w64-mingw32)	1m 58s
mingw-build (--host=i686-w64-mingw32)	1m 58s
	26m 14s

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