fix: can't show duckdb table names in the "SEE TABLE SCHEMA" dropdown list

[forestlzj]

fix bug: #21210
the previous approach inspector.get_table_names() always gets table name in default "main" schema instead of getting table name from an input schema specified in superset UI

SUMMARY

fix bug #21210: can't show duckdb table names in the "SEE TABLE SCHEMA" dropdown list

TESTING INSTRUCTIONS

1. create a duckdb file connection
2. create a schema in the duckdb. e.g. "foo"
3. create a table "tab1" in schema "foo"
4. in sql lab, choose the duckdb connection, choose schema "foo" or any other
5. it is expected table "tabi1" (or other) in the "SEE TABLE SCHEMA" dropdown list , before fixing , it is not showed anything

after installing duckdb_engine >=0.6.3 and the applying the fix in the PR, in step5, it can show the expected tables

ADDITIONAL INFORMATION

• [Y] Has associated issue: fix duckdb - unable to list the table schema #21210
• [ N] Required feature flags:
• [ N] Changes UI
• [ N] Includes DB Migration (follow approval process in SIP-59)
  • [ N] Migration is atomic, supports rollback & is backwards-compatible
  • [ N] Confirm DB migration upgrade and downgrade tested
  • [ N] Runtime estimates and downtime expectations provided
• [ N] Introduces new feature or API
• [N ] Removes existing feature or API

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Codecov Report

Merging #21495 (dcf61cf) into master (b739e27) will not change coverage.
The diff coverage is 0.00%.

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  Lines       68492    68492           
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  Hits        45663    45663           
  Misses      20967    20967           
  Partials     1862     1862           

Flag	Coverage Δ
hive	53.08% <0.00%> (ø)
mysql	78.20% <0.00%> (ø)
postgres	78.27% <0.00%> (ø)
presto	52.98% <0.00%> (ø)
python	81.41% <0.00%> (ø)
sqlite	76.76% <0.00%> (ø)
unit	51.05% <0.00%> (ø)

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Impacted Files	Coverage Δ
superset/db_engine_specs/duckdb.py	75.86% <0.00%> (ø)

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[zhaoyongjie]

Tested by DuckDB 5.0 and the latest engine, it works for me. Thanks for the fixing!