ci: fix coverage report

[Glonee]

I noticed that the coverage report is not working in quic-go since last week, due to:

quic-go/.github/workflows/unit.yml

Line 47 in cec79d3

files: coverage.txt coverage-root.txt

Actually we should use a comma instead of a space to separate files here.

[marten-seemann]

Looks correct: https://github.com/codecov/codecov-action#arguments

Thank you @Glonee!

[codecov]

Codecov Report

Merging #3837 (f5d6209) into master (da198b7) will increase coverage by 0.06%.
The diff coverage is 72.37%.

@@            Coverage Diff             @@
##           master    #3837      +/-   ##
==========================================
+ Coverage   83.92%   83.99%   +0.06%     
==========================================
  Files         142      146       +4     
  Lines       14208    14290      +82     
==========================================
+ Hits        11924    12002      +78     
+ Misses       1850     1849       -1     
- Partials      434      439       +5     

Impacted Files	Coverage Δ
quicvarint/varint.go	76.47% <ø> (+9.23%)	⬆️
transport.go	63.52% <50.00%> (-1.00%)	⬇️
sys_conn_buffers.go	57.78% <57.78%> (ø)
sys_conn_buffers_write.go	64.44% <64.44%> (ø)
sys_conn_helper_linux.go	81.25% <81.25%> (ø)
http3/roundtrip.go	89.93% <100.00%> (+0.80%)	⬆️
sys_conn_helper_nonlinux.go	100.00% <100.00%> (ø)
sys_conn_oob.go	73.68% <100.00%> (+4.57%)	⬆️
sys_conn_windows.go	100.00% <100.00%> (+27.27%)	⬆️