Updated issue sql parts that were errantly not excluding pull_requests; fixed 2 typos where `not null` were expressed as `notnull` and added `issues.pull_request IS NOT NULL` in four places where pull requests are being counted using the issues table partly.
Updated issue sql parts that were errantly not excluding pull_requests; fixed 2 typos where `not null` were expressed as `notnull` and added `issues.pull_request IS NOT NULL` in four places where pull requests are being counted using the issues table partly.

OSSHealth/ghdata,OSSHealth/ghdata,OSSHealth/ghdata