Arrays are not sent correctly due to not using [] after variable name

GitLab's API documentation: https://docs.gitlab.com/ee/api/#array

array types

import_sources is a parameter of type array:

curl --request POST --header "PRIVATE-TOKEN: <your_access_token>" \
-d "import_sources[]=github" \
-d "import_sources[]=bitbucket" \
"https://gitlab.example.com/api/v4/some_endpoint"

So when we send array values we most append [] to the array's variable name.

This has caused issues like:

• Trying to Fetch multiple ProjectIssues in a single batch call returns only the last ProjectIssue specified in the list #1407
• List groups only skips the last id provided in skip_groups #1256