docs: fix AttributeError when run in parallel
docs: fix AttributeError when run in parallel

- AttributeError: 'BuildEnvironment' object has no attribute 'bioconda_lint_checks'
- Does not occur with SPHINXOPTS='-j1' (i.e., current CI config).

bioconda/bioconda-utils,bioconda/bioconda-utils,bioconda/bioconda-utils