fix(builtins): skip unenumerable vars in set builtin

[reubeno]

No description provided.

[github-actions]

Test Results

    2 files      9 suites   1m 18s ⏱️
  585 tests   585 ✅ 0 💤 0 ❌
1 156 runs  1 156 ✅ 0 💤 0 ❌

Results for commit 2b029e5.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
clone_shell_object	16.50 μs	16.39 μs	-0.11 μs	⚪ Unchanged
eval_arithmetic	0.19 μs	0.19 μs	-0.00 μs	⚪ Unchanged
expand_one_string	1.63 μs	1.65 μs	0.02 μs	⚪ Unchanged
for_loop	33.28 μs	32.67 μs	-0.61 μs	⚪ Unchanged
function_call	3.72 μs	3.39 μs	-0.33 μs	🟢 -8.84%
instantiate_shell	47.81 μs	48.27 μs	0.46 μs	⚪ Unchanged
instantiate_shell_with_init_scripts	24647.77 μs	24270.80 μs	-376.97 μs	⚪ Unchanged
parse_bash_completion	1700.81 μs	1677.38 μs	-23.44 μs	🟢 -1.38%
parse_sample_script	2.21 μs	2.15 μs	-0.07 μs	🟢 -3.03%
run_echo_builtin_command	16.75 μs	16.09 μs	-0.66 μs	⚪ Unchanged
run_one_external_command	1976.61 μs	1724.38 μs	-252.23 μs	🟢 -12.76%

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-core/src/builtins/set.rs	🟠 60.69%	🟠 59.66%	🔴 -1.03%
brush-core/src/jobs.rs	🔴 37.07%	🔴 43.1%	🟢 6.03%
brush-core/src/shell.rs	🟢 82.27%	🟢 82.4%	🟢 0.13%
Overall Coverage	🟢 76.96%	🟢 77.04%	🟢 0.08%

Minimum allowed coverage is 70%, this run produced 77.04%