Replace #[deny] with #[warn]

[jedel1043]

See https://rust-unofficial.github.io/patterns/anti_patterns/deny-warnings.html for context.

This also improves a bit the prototyping experience, since now we can compile and run with warnings even if there are missing docs or suboptimal code patterns.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	95,574	95,574	0
Passed	75,165	75,165	0
Ignored	19,494	19,494	0
Failed	915	915	0
Panics	0	0	0
Conformance	78.65%	78.65%	0.00%

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (a7ffa00) 49.79% compared to head (51487ad) 49.79%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3309      +/-   ##
==========================================
- Coverage   49.79%   49.79%   -0.01%     
==========================================
  Files         441      441              
  Lines       43081    43081              
==========================================
- Hits        21452    21451       -1     
- Misses      21629    21630       +1     

Files	Coverage Δ
boa_ast/src/lib.rs	75.00% <ø> (ø)
boa_cli/src/main.rs	0.61% <ø> (ø)
boa_engine/src/lib.rs	73.33% <ø> (ø)
boa_gc/src/lib.rs	99.45% <ø> (ø)
boa_icu_provider/src/lib.rs	100.00% <ø> (ø)
boa_interner/src/lib.rs	87.37% <ø> (ø)
boa_macros/src/lib.rs	0.00% <ø> (ø)
boa_profiler/src/lib.rs	66.66% <ø> (ø)
boa_tester/src/main.rs	0.00% <ø> (ø)
boa_wasm/src/lib.rs	0.00% <ø> (ø)

... and 1 file with indirect coverage changes

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[HalidOdat]

Nice change! :)