Fix(#39): remove NAs before type casting

[andybeet]

Justification

This issue was previously fixed but it appears the database has introduced additional data issues. Several STOCK_AREA values are either NAs or "NA". This warnings causes GitHub workflows to fail (although we could prevent workflows from failing on a warning, i'd prefere to fix the code). These NAs have been filtered out prior to type casting to numeric. Issue 39 was reopened.

Fixes #39

Types of changes

What types of changes does this pull request introduce? Put an x in the boxes that apply.
This will inform the new release number.

• Fix (non-breaking change which fixes a bug)
• Feature (non-breaking change which adds or changes functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other change (if none of the other choices apply)

Reviewer instructions

Do the following on dev and this branch.

• Connect to the database eg. channel <- dbutils::connect_to_database("server", "user")
• get_herring_data(channel)
  The coercion warning should be fixed

Formatting

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Code submitted in this pull request will be automatically checked for correct formatting.

[BBeltz1]

code looks appropriate, coercion warning has been resolved on branch