chore: switch to testing on debian:testing

[reubeno]

This should give us a more recent version of the bash oracle to use.

[github-actions]

Test Results

    2 files      9 suites   1m 36s ⏱️
  669 tests   669 ✅ 0 💤 0 ❌
1 324 runs  1 324 ✅ 0 💤 0 ❌

Results for commit ef26aec.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
clone_shell_object	18.21 μs	18.04 μs	-0.17 μs	🟢 -0.94%
eval_arithmetic	0.17 μs	0.17 μs	0.00 μs	⚪ Unchanged
expand_one_string	1.82 μs	1.79 μs	-0.02 μs	⚪ Unchanged
for_loop	22.04 μs	22.02 μs	-0.01 μs	⚪ Unchanged
function_call	2.33 μs	2.31 μs	-0.02 μs	⚪ Unchanged
instantiate_shell	57.48 μs	57.33 μs	-0.15 μs	⚪ Unchanged
instantiate_shell_with_init_scripts	21469.53 μs	21308.49 μs	-161.04 μs	⚪ Unchanged
parse_bash_completion	1676.24 μs	1660.30 μs	-15.94 μs	⚪ Unchanged
parse_sample_script	1.75 μs	1.77 μs	0.02 μs	🟠 +1.37%
run_echo_builtin_command	15.33 μs	15.45 μs	0.12 μs	⚪ Unchanged
run_one_external_command	2061.52 μs	2032.37 μs	-29.15 μs	🟢 -1.41%
tokenize_sample_script	2.92 μs	2.91 μs	-0.00 μs	⚪ Unchanged

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-core/src/builtins/mapfile.rs	🟢 76.6%	🟢 76.84%	🟢 0.24%
brush-core/src/builtins/read.rs	🟠 66.27%	🟠 65.87%	🔴 -0.4%
brush-core/src/commands.rs	🟢 87.21%	🟢 86.97%	🔴 -0.24%
brush-core/src/interp.rs	🟢 91.55%	🟢 91.65%	🟢 0.1%
brush-core/src/options.rs	🟢 93.48%	🟢 92.39%	🔴 -1.09%
Overall Coverage	🟢 75.72%	🟢 75.72%	⚪ 0%

Minimum allowed coverage is 70%, this run produced 75.72%