CI: cleanup wasm32 target dir before pr benchmark

[sergejparity]

Cleanup target/wasm32-wasi dir before benchmarking PR branch to prevent artifact copying errors.

[paritytech-cicd-pr]

BENCHMARKS

	NATIVE			WASMTIME
BENCHMARK	MASTER	PR	DIFF	MASTER	PR	DIFF	WASMTIME OVERHEAD
execute/ count_until	887.30µs	1.25ms	🔴 58.62%	2.38ms	2.38ms	⚪ 0.00%	🟡 91%
execute/ factorial_iterative	400.68ns	400.83ns	⚪ 0.11%	993.93ns	993.82ns	⚪ 0.01%	🔴 148%
execute/ factorial_recursive	756.83ns	758.21ns	⚪ 0.41%	1.55µs	1.56µs	⚪ 0.13%	🔴 105%
execute/ fib_iterative	1.79ms	1.82ms	⚪ 1.36%	5.11ms	5.11ms	⚪ -0.09%	🔴 180%
execute/ fib_recursive	6.79ms	6.85ms	⚪ 0.33%	14.14ms	14.04ms	⚪ -0.89%	🔴 105%
execute/ global_bump	1.43ms	1.43ms	⚪ -0.12%	3.64ms	3.63ms	⚪ -0.18%	🔴 153%
execute/ host_calls	31.79µs	31.90µs	⚪ 0.26%	45.02µs	45.02µs	⚪ -0.14%	🟢 41%
execute/ memory_fill	1.64ms	1.54ms	🟢 -6.39%	4.33ms	4.32ms	⚪ -0.15%	🔴 182%
execute/ memory_sum	1.52ms	1.52ms	⚪ 0.01%	4.37ms	4.36ms	⚪ -0.17%	🔴 187%
execute/ memory_vec_add	3.02ms	3.02ms	⚪ 0.00%	8.98ms	8.95ms	⚪ -0.38%	🔴 196%
execute/ recursive_is_even	1.29ms	1.28ms	⚪ -0.59%	2.55ms	2.53ms	⚪ -0.40%	🟡 97%
execute/ recursive_ok	172.83µs	172.82µs	⚪ -0.03%	350.19µs	349.10µs	⚪ -0.38%	🔴 102%
execute/ recursive_scan	212.00µs	212.12µs	⚪ -0.14%	453.98µs	452.19µs	⚪ -0.36%	🔴 113%
execute/ recursive_trap	17.20µs	17.20µs	⚪ -0.11%	34.83µs	34.81µs	⚪ -0.17%	🔴 102%
execute/ regex_redux	650.87µs	650.69µs	⚪ -0.09%	1.60ms	1.60ms	⚪ -0.04%	🔴 145%
execute/ rev_complement	585.34µs	593.90µs	🔴 1.55%	1.55ms	1.57ms	🔴 1.25%	🔴 165%
execute/ tiny_keccak	454.12µs	459.15µs	⚪ 0.62%	1.43ms	1.41ms	🟢 -2.05%	🔴 206%
execute/ trunc_f2i	1.07ms	1.07ms	⚪ 0.00%	2.76ms	2.72ms	🟢 -1.21%	🔴 155%
instantiate/ wasm_kernel	66.78µs	67.98µs	⚪ 2.04%	127.97µs	96.33µs	🟢 -24.59%	🟢 42%
translate/ wasm_kernel	4.84ms	4.85ms	⚪ 0.28%	9.60ms	9.83ms	🔴 2.35%	🔴 103%

Link to pipeline

[codecov-commenter]

Codecov Report

Merging #506 (00abd9a) into master (d31ca3f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #506   +/-   ##
=======================================
  Coverage   79.23%   79.23%           
=======================================
  Files          74       74           
  Lines        6313     6313           
=======================================
  Hits         5002     5002           
  Misses       1311     1311           

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[Robbepop]

LGTM, thank you @sergejparity for the quick fix!