Add CI workflow running integration tests with irctest

[progval]

Summary

This adds a new CI workflows which uses the irctest test suite to run integration test on the C2S protocol

Rationale

It will help detect regressions, such as the ones fixed by:

• https://github.com/inspircd/inspircd/commit/7c25da154eb5fbc4b736b533587a2850c7624ae7
• https://github.com/inspircd/inspircd/commit/023ca96054191b66643425d673acb66c08fa1048

Actually running the build also detects link issues (it happened once or twice in the past)

Testing Environment

N/A

Checks

I have ensured that:

• [x] This pull request does not introduce any incompatible API changes.
• [x] If ABI changes have been made I have incremented MODULE_ABI in moduledefs.h.
• [x] I have documented any features added by this pull request.