Reduce severity for channel handler 'no channel available' logs

Current situation

Channel handlers (for agents and ssh execution environments) emit logs when they cannot make an offer:

[2023-06-07 18:57:56,509] WARNING in sshchannel: Could not find environment matching request ['windows'] in namespace default.

This is a good thing, but the WARNING severity is to high, and may confuse users.

The log message severity should be INFO, as in:

[2023-06-07 18:57:56,509] INFO in sshchannel: Could not find environment matching request ['windows'] in namespace default.