Fix multiline for execute steps

[adrianburusdbt]

Problem
The regex pattern used for validation (^\sdbt\s+....$) doesn't match newline characters with .*, causing multi-line commands like the following to fail validation:

execute_steps = [<<-EOT
dbt run --select    
  my_project,config.materialized:view,state:modified,tag:my_tag    
  my_project,config.materialized:table,tag:my_tag    
  my_project,config.materialized:incremental,tag:my_tag
EOT
]

Solution
Normalize commands by replacing newlines (\n and \r) with spaces before running the regex validation. This matches how dbt Cloud interprets these commands - newlines are treated as whitespace separators.

[vladmld]

👍🏼