fix: fix group by cube with join panic assert

[lichuang]

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Summary

fix: fix group by bug

• Fixes bug: group by cube with join cause panic #14500

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

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This change is 

[what-the-diff]

PR Summary

• New Test File Added
  A new test file named issue_14500.test has been incorporated into the tests/sqllogictests/suites/base/issues directory. This helps to improve the robustness of the project by increasing the range of tests it can perform.

• Updated Assertion Statement in physical_aggregate_expand.rs
  The code within the physical_aggregate_expand.rs file was updated, specifically the assertion statement at line 55. This modification now allows the use of nullable data types which provides more flexibility in the system.

• Expansion of output_fields Vector in physical_aggregate_expand.rs
  Another adjustment was made in the physical_aggregate_expand.rs file which involved adding a new field into the output_fields vector at line 56. This addition could potentially increase and aid the versatility of data handling within the program.