[CT-2375] [Bug] dbtRunner instances share the callbacks across instances when no callbacks are passed

[chamini2]

Is this a new bug in dbt-core?

• I believe this is a new bug in dbt-core
• I have searched the existing issues, and I could not find an existing issue for this bug

Current Behavior

from dbt.cli.main import dbtRunner, list
from dbt.events.base_types import EventMsg

def print_callback(event: EventMsg):
    print("Got an event:", event.info.name)

dbt = dbtRunner()
dbt.callbacks.append(print_callback)

dbt2 = dbtRunner()
dbt2.invoke(['list'])   # this prints the event names

example run:

❯ python runner.py
16:32:42  Running with dbt=1.5.0-b5
Got an event: MainReportVersion
Got an event: MainReportArgs
16:32:42  [WARNING]: Deprecated functionality
The `target-path` config in `dbt_project.yml` has been deprecated, and will no
longer be supported in a future version of dbt-core. If you wish to write dbt
artifacts to a custom directory, please use the --target-path CLI flag or
DBT_TARGET_PATH env var instead.
Got an event: ConfigTargetPathDeprecation
Got an event: SendingEvent
Got an event: SendingEvent
Got an event: SendingEvent
Got an event: StateCheckVarsHash
Got an event: PartialParsingEnabled
Got an event: PartialParsingSkipParsing
Got an event: SendingEvent
Got an event: SendingEvent
16:32:42  Found 4 models, 0 tests, 0 snapshots, 0 analyses, 309 macros, 0 operations, 0 seed files, 0 sources, 0 exposures, 0 metrics, 0 groups
Got an event: FoundStats
Got an event: SendingEvent
simple_test.base.model_a
simple_test.base.model_b
simple_test.python.model_c
simple_test.model_d
Got an event: CommandCompleted
Got an event: SendingEvent
Got an event: FlushEvents

Expected Behavior

dbtRunner instances should be isolated from one another.

Steps To Reproduce

See current behavior

Relevant log output

No response

Environment

- OS: macOS Ventura
- Python: Python 3.8.13
- dbt: 1.5.0-b5

Which database adapter are you using with dbt?

postgres

Additional Context

https://stackoverflow.com/questions/366422/how-can-i-avoid-issues-caused-by-pythons-early-bound-default-parameters-e-g-m

[jtcohen6]

@chamini2 Thanks for best-testing, and for the quick PR !! :)