fix: SQLAlchemy coercing subquery warning on RLS

[dpgaspar]

SUMMARY

Fix for SQLAlchemy warning:

/usr/local/lib/python3.8/site-packages/superset/security/manager.py:1499: SAWarning: Coercing Subquery object into a select() for use in IN(); please pass a select() construct explicitly
  RowLevelSecurityFilter.id.in_(regular_filter_roles),

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #21257 (951bee1) into master (b354f22) will decrease coverage by 0.17%.
The diff coverage is n/a.

❗ Current head 951bee1 differs from pull request most recent head 0fe9eb7. Consider uploading reports for the commit 0fe9eb7 to get more accurate results

@@            Coverage Diff             @@
##           master   #21257      +/-   ##
==========================================
- Coverage   66.46%   66.28%   -0.18%     
==========================================
  Files        1784     1784              
  Lines       68162    68162              
  Branches     7265     7265              
==========================================
- Hits        45302    45183     -119     
- Misses      20991    21110     +119     
  Partials     1869     1869              

Flag	Coverage Δ
hive	?
mysql	80.87% <ø> (ø)
postgres	80.93% <ø> (ø)
presto	?
python	81.04% <ø> (-0.37%)	⬇️
sqlite	79.44% <ø> (ø)
unit	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/security/manager.py	95.07% <ø> (ø)
superset/db_engines/hive.py	0.00% <0.00%> (-85.19%)	⬇️
superset/db_engine_specs/hive.py	71.09% <0.00%> (-16.02%)	⬇️
superset/db_engine_specs/presto.py	81.32% <0.00%> (-6.63%)	⬇️
superset/models/sql_lab.py	74.90% <0.00%> (-2.00%)	⬇️
superset/initialization/__init__.py	89.96% <0.00%> (-1.74%)	⬇️
superset/connectors/sqla/models.py	89.79% <0.00%> (-0.71%)	⬇️
superset/db_engine_specs/base.py	87.89% <0.00%> (-0.32%)	⬇️
superset/models/core.py	88.65% <0.00%> (-0.24%)	⬇️
superset/utils/core.py	90.23% <0.00%> (-0.12%)	⬇️

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