If non-default value is passed for injectable param, rewriter throws SyntaxError

[cisaacstern]

As described in pangeo-forge/pangeo-forge-recipes#587 (comment). Per @yuvipanda's suggestion on the same thread, the rewriter should instead allow this type of manual override, and instead of raising an error, inject no value in this case.

[yuvipanda]

pangeo-forge-runner/pangeo_forge_runner/recipe_rewriter.py

Line 144 in e3c2dd1

node.keywords += [

is where the fix should be. There should be a conditional - if the keyword already exists, we should choose to either first delete it, or ignore completely.