test: Add snapshot test for dm_squash_to_tbl()

[Copilot]

The deprecation warning for dm_squash_to_tbl() was incorrectly referencing the parameter name recursive instead of .recursive when suggesting users migrate to dm_flatten_to_tbl().

The warning message previously said:

Please use `recursive = TRUE` in `dm_flatten_to_tbl()` instead.

But the actual parameter name in dm_flatten_to_tbl() is .recursive (with a dot prefix), so the corrected message now says:

Please use `.recursive = TRUE` in `dm_flatten_to_tbl()` instead.

This ensures users get the correct parameter name when following the deprecation guidance.

Additionally, added a snapshot test to verify the deprecation warning message is correct and prevent future regressions.

Fixes #1364.

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[krlmlr]

@copilot: Add a snapshot test.

[krlmlr]

Add a snapshot test.

[Copilot]

@copilot: Add a snapshot test.

Added a snapshot test for the dm_squash_to_tbl() deprecation warning to verify that the correct parameter name .recursive is shown in the message. The test will capture the warning text to prevent future regressions. Commit a7b3fc1.

[Copilot]

Add a snapshot test.

Snapshot test for dm_squash_to_tbl() deprecation warning has already been added in commit a7b3fc1. The test verifies that the correct parameter name .recursive is shown in the deprecation message.