Add failing test for stopped transceivers

[k0nserv]

Description

A small failing test were upon stopping a transceiver it is not rejected in the following offer.

[codecov]

Codecov Report

Merging #2274 (1ac8c71) into master (dd41fbf) will decrease coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2274      +/-   ##
==========================================
- Coverage   77.29%   77.19%   -0.10%     
==========================================
  Files          87       87              
  Lines        9197     9197              
==========================================
- Hits         7109     7100       -9     
- Misses       1654     1660       +6     
- Partials      434      437       +3     

Flag	Coverage Δ
go	78.95% <ø> (-0.11%)	⬇️
wasm	70.16% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
internal/mux/mux.go	84.78% <0.00%> (-4.35%)	⬇️
sctptransport.go	77.15% <0.00%> (-0.75%)	⬇️
peerconnection.go	77.41% <0.00%> (-0.18%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update dd41fbf...1ac8c71. Read the comment docs.