Add Nextflow and nf-test as dependencies to nf-core

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General instructions

If this PR adds or updates a recipe, use "Add" or "Update" appropriately as the first word in its title.
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Instructions for avoiding API, ABI, and CLI breakage issues

Conda is able to record and lock (a.k.a. pin) dependency versions used at build time of other recipes. This way, one can avoid that expectations of a downstream recipe with regards to API, ABI, or CLI are violated by later changes in the recipe. If not already present in the meta.yaml, make sure to specify run_exports (see here for the rationale and comprehensive explanation). Add a run_exports section like this:

build:
  run_exports:
    - ...

with ... being one of:

Case	run_exports statement
semantic versioning	`{{ pin_subpackage("myrecipe", max_pin="x") }}`
semantic versioning (0.x.x)	`{{ pin_subpackage("myrecipe", max_pin="x.x") }}`
known breakage in minor versions	`{{ pin_subpackage("myrecipe", max_pin="x.x") }}` (in such a case, please add a note that shortly mentions your evidence for that)
known breakage in patch versions	`{{ pin_subpackage("myrecipe", max_pin="x.x.x") }}` (in such a case, please add a note that shortly mentions your evidence for that)
calendar versioning	`{{ pin_subpackage("myrecipe", max_pin=None) }}`

while replacing "myrecipe" with either name if a name|lower variable is defined in your recipe or with the lowercase name of the package in quotes.

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bioconda / bioconda-recipes