Add Node 21 to leak tests

[ardatan]

No description provided.

[github-actions]

🚀 Snapshot Release (alpha)

The latest changes of this PR are available as alpha on npm (based on the declared changesets):

Package	Version	Info
@whatwg-node/fetch	0.9.14-alpha-20231025105421-51d36bc	npm ↗︎ unpkg ↗︎
@whatwg-node/node-fetch	0.5.0-alpha-20231025105421-51d36bc	npm ↗︎ unpkg ↗︎

[github-actions]

✅ Benchmark Results

     ✓ no-errors
     ✓ expected-result

     checks.........................: 100.00% ✓ 240026      ✗ 0     
     data_received..................: 24 MB   788 kB/s
     data_sent......................: 9.6 MB  320 kB/s
     http_req_blocked...............: avg=1.52µs   min=700ns   med=1.2µs    max=1.12ms   p(90)=1.9µs    p(95)=2.29µs  
     http_req_connecting............: avg=4ns      min=0s      med=0s       max=593.83µs p(90)=0s       p(95)=0s      
     http_req_duration..............: avg=172.62µs min=84µs    med=138.2µs  max=21.97ms  p(90)=212.51µs p(95)=267.45µs
       { expected_response:true }...: avg=172.62µs min=84µs    med=138.2µs  max=21.97ms  p(90)=212.51µs p(95)=267.45µs
     http_req_failed................: 0.00%   ✓ 0           ✗ 120013
     http_req_receiving.............: avg=23.63µs  min=10.9µs  med=18.1µs   max=11.51ms  p(90)=34.3µs   p(95)=38µs    
     http_req_sending...............: avg=7.84µs   min=3.8µs   med=5.6µs    max=4.49ms   p(90)=10.2µs   p(95)=13µs    
     http_req_tls_handshaking.......: avg=0s       min=0s      med=0s       max=0s       p(90)=0s       p(95)=0s      
     http_req_waiting...............: avg=141.14µs min=64.9µs  med=110.6µs  max=21.38ms  p(90)=175.11µs p(95)=222.61µs
     http_reqs......................: 120013  4000.225922/s
     iteration_duration.............: avg=243.59µs min=128.9µs med=201.31µs max=22.11ms  p(90)=301.71µs p(95)=367.02µs
     iterations.....................: 120013  4000.225922/s
     vus............................: 0       min=0         max=1   
     vus_max........................: 1       min=1         max=1