test: add case: specific channel specification under requirements, w/ channel_sources and tests specified

[dlaehnemann]

This comes from an attempt to build a conda-forge package that references dependencies from the bioconda channel. The syntax seems to work for building, but the channel then isn't found during testing. Thus, this test case includes a tests: section.

Generally, if this channel specification works out with both building and testing, we can use this to consistently fix a number of conda-forge packages that added bioconda package dependencies at some point (usually r- packages from CRAN that added bioconductor- package dependencies).

[wolfv]

Just to note - this could/might work in the test section. It will NOT work as part of the run dependnecies of a package as channel-specific run dependencies need the :: or [ ... ] syntax, whcih is currently not emitted to the repodata.json.

That will likely change with repodata v3, which is in a CEP that should be soon voted on.

[dlaehnemann]

Would this work in the build: and host: sections under requirements:, as these are only used when building the package, and should have pulled the respective packages in at that time? That might already solve some of our use cases.

Also, do you have a cross-link to the CEP you mention? I had a quick look at some open PRs on the CEPS repo and couldn't identify it.