style: include if_not_else

[vil02]

Pull Request Template

Description

This PR removes if_not_else from the list of from the list of suppressed lints.

Continuation of #743.

Checklist:

• I ran bellow commands using the latest version of rust nightly.
• I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• I ran cargo fmt just before my last commit.
• I ran cargo test just before my last commit and all tests passed.
• I added my algorithm to the corresponding mod.rs file within its own folder, and in any parent folder(s).
• I added my algorithm to DIRECTORY.md with the correct link.
• I checked COUNTRIBUTING.md and my code follows its guidelines.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 53.75000% with 37 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.32%. Comparing base (7d7d716) to head (b8b5a56).

Files with missing lines	Patch %	Lines
src/data_structures/rb_tree.rs	43.75%	36 Missing ⚠️
src/math/modular_exponential.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #918      +/-   ##
==========================================
- Coverage   95.33%   95.32%   -0.01%     
==========================================
  Files         319      319              
  Lines       20901    20899       -2     
==========================================
- Hits        19925    19923       -2     
  Misses        976      976              

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[siriak]

Looks good, thanks!