fix(return): exit code when stderr is not writable

[reubeno]

Resolves #973

[github-actions]

Test Results

    3 files     32 suites   12m 8s ⏱️
1 892 tests 1 892 ✅ 0 💤 0 ❌
5 648 runs  5 648 ✅ 0 💤 0 ❌

Results for commit b51b86e.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
clone_shell_object	16.82 μs	16.92 μs	0.10 μs	⚪ Unchanged
eval_arithmetic	0.15 μs	0.15 μs	0.00 μs	⚪ Unchanged
expand_one_string	1.65 μs	1.63 μs	-0.02 μs	⚪ Unchanged
for_loop	22.69 μs	22.60 μs	-0.09 μs	⚪ Unchanged
function_call	2.73 μs	2.53 μs	-0.20 μs	⚪ Unchanged
instantiate_shell	52.74 μs	52.37 μs	-0.37 μs	⚪ Unchanged
instantiate_shell_with_init_scripts	25566.63 μs	26556.75 μs	990.12 μs	🟠 +3.87%
parse_bash_completion	2038.81 μs	2054.53 μs	15.72 μs	🟠 +0.77%
parse_sample_script	1.96 μs	1.92 μs	-0.04 μs	⚪ Unchanged
run_echo_builtin_command	16.10 μs	16.01 μs	-0.09 μs	⚪ Unchanged
tokenize_sample_script	3.46 μs	3.51 μs	0.06 μs	🟠 +1.65%

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-builtins/src/return_.rs	🟢 93.75%	🟢 100%	🟢 6.25%
brush-core/src/expansion.rs	🟢 94.33%	🟢 94.25%	🔴 -0.08%
brush-core/src/results.rs	🟢 83.33%	🟢 80.16%	🔴 -3.17%
Overall Coverage	🟢 74.32%	🟢 74.3%	🔴 -0.02%

Minimum allowed coverage is 70%, this run produced 74.3%

Test Summary: bash-completion test suite

Outcome	Count	Percentage
✅ Pass	1556	73.78
❗️ Error	19	0.90
❌ Fail	180	8.53
⏩ Skip	339	16.07
❎ Expected Fail	13	0.62
✔️ Unexpected Pass	2	0.09
📊 Total	2109	100.00