[Bug]: Changes always detected in SSH fleet configurations

[jvstme]

Steps to reproduce

1. Apply an SSH fleet configuration.
2. Apply the same configuration again.

Actual behaviour

dstack says that configuration changes were detected.

> dstack apply -f fleets/on-prem.dstack.yml 
 Project        ilya                      
 User           admin                     
 Configuration  fleets/on-prem.dstack.yml 
 Type           fleet                     
 Fleet type     ssh                       
 Nodes          1                         
 Placement      any                       

Fleet on-prem does not exist yet.
Create the fleet? [y/n]: y
 FLEET    INSTANCE  BACKEND       RESOURCES                  PRICE  STATUS  CREATED 
 on-prem  0         ssh (remote)  2xCPU, 1GB, 35.2GB (disk)  $0.0   idle    23:08   

> dstack apply -f fleets/on-prem.dstack.yml
 Project        ilya                      
 User           admin                     
 Configuration  fleets/on-prem.dstack.yml 
 Type           fleet                     
 Fleet type     ssh                       
 Nodes          1                         
 Placement      any                       

Found fleet on-prem. Configuration changes detected.
Re-create the fleet? [y/n]:

Expected behaviour

dstack warns that that configuration hasn't changed.

dstack version

0.18.36

Server logs

Additional information

No response

[un-def]

The issue was reintroduced with #2579