fix: use tuple membership check instead of substring match in selection_arg

[kalluripradeep]

Fixes #12539

What changed

Fixed a one-character bug in core/dbt/task/show.py and
core/dbt/task/compile.py where self.selection_arg[0] was used
instead of self.selection_arg in the result filtering loop.

Why

self.selection_arg is a tuple like ('my_model_show',).

Using result.node.name in self.selection_arg[0] does a substring
check on a string, not a membership check on the tuple:

# Buggy behaviour:
'show' in 'my_model_show'   # True  ← wrong, show is a substring
'show' in ('my_model_show',) # False ← correct, show is not in the tuple

So any model whose name contained a common substring like show,
model, or my would incorrectly match other nodes during result
filtering, causing inconsistent behaviour depending on the model name.

How I fixed it

Removed the [0] index in both files so the check becomes a proper
tuple membership check:

# Before:
if result.node.name in self.selection_arg[0]:

# After:
if result.node.name in self.selection_arg:

Files changed

• core/dbt/task/show.py
• core/dbt/task/compile.py