do not ignore error when walk dir in pkger

[alovak]

What:

• handle (do not ignore) error from the function that adds migration files into pkger

Why:

Currently, we ignore the error when pkger walks the migration directory and the migration file name does not match the expected format. When such happens it stops adding the rest of the files. In our case with manual migrations, we named the file in a way so golang-migrate will ignore it: we just removed .up part. But, we didn't know that we have one more layer of file format checking :(

P.S. we should not check file name format here and delegate it to golang-migrate

[codecov-commenter]

Codecov Report

Merging #230 (ae76db3) into master (19fece7) will decrease coverage by 0.16%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #230      +/-   ##
==========================================
- Coverage   77.84%   77.68%   -0.17%     
==========================================
  Files          29       29              
  Lines         930      932       +2     
==========================================
  Hits          724      724              
- Misses        161      162       +1     
- Partials       45       46       +1     

Impacted Files	Coverage Δ
database/pkger.go	55.10% <33.33%> (-2.35%)	⬇️

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