fix: only update pending incoming connections if connection accepted

[achingbrain]

The afterUpgradeInbound function decrements the count of pending (e.g. not upgraded yet) incoming connections, so only invoke that method if we actually accepted the connection, otherwise we decrement a counter that was never incremented.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works