GitHub Actions CI now enabled for INN pull requests

[Julien ÉLIE]

Hi Russ,

> I've enabled some simple GitHub Actions testing for all pull requests and
> pushes for the main branch.  This does the same checks that we are doing
> when generating snapshots: builds with various options with warnings
> enabled plus running the (somewhat meager, alas) test suite.  That should
> at least give us a basic sanity check for pull requests.

Works pretty fine, thanks!

Having a look at GitHub possibilities, I see we can add code scanning 
for common vulnerabilities and coding errors (like CodeQL Analysis). 
Has anyone tested it?  Is it worthwhile?

-- 
Julien ÉLIE

« Vous savez, les idées, elles sont dans l'air. Il suffit que quelqu'un
   vous en parle de trop près, pour que vous les attrapiez ! » (Raymond
   Devos)