update_pinnings: Fail if build string is incomplete
update_pinnings: Fail if build string is incomplete

With bypass_env_check we get invalid build string like in
"r-dimsum=1.1.3=r>=36_0". conda-build special-cases python/r-base/...
deps but with bypass_env_check it cannot resolve the actual versions.
In most cases the recipe then needs manual editing anyway because it
should use build/skip rather than constrain versions in requirements.

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