completions to use new Jedi get_names method

[moselhy]

For #10632

jedi.api.names has been deprecated, use new syntax instead.

• note I could have used the Script object initialized in the lines right below the change, but I went the safe route since the method enclosing the change returns pre-emptively

[ghost]

All CLA requirements met.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0%. Comparing base (b8c66c4) to head (d446230).
⚠️ Report is 2347 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff           @@
##           main   #15791    +/-   ##
======================================
- Coverage    46%       0%   -47%     
======================================
  Files        12        7     -5     
  Lines       429       14   -415     
  Branches     60        1    -59     
======================================
- Hits        201        0   -201     
+ Misses      216       14   -202     
+ Partials     12        0    -12     

see 5 files with indirect coverage changes

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