Fix test_receiver_interceptor_jitter on Ubuntu

[k0nserv]

A previous fix for this issue has proven not to work. With this we
make time entirely deterministic in this test, a practice that we should
use in other tests if successful here.

[k0nserv]

I initially introduced this problem in webrtc-rs/interceptor#5

[algesten]

Merge away.

[k0nserv]

Wanna see if CI passes first :)

[codecov]

Codecov Report

Merging #258 (17819b6) into master (1614c3b) will decrease coverage by 0.00%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master     #258      +/-   ##
==========================================
- Coverage   56.05%   56.04%   -0.01%     
==========================================
  Files         500      500              
  Lines       46523    46525       +2     
  Branches    12714    12714              
==========================================
- Hits        26077    26075       -2     
+ Misses       9922     9921       -1     
- Partials    10524    10529       +5     

Impacted Files	Coverage Δ
interceptor/src/report/receiver/receiver_test.rs	65.97% <50.00%> (-0.09%)	⬇️
webrtc/src/mux/mux_func.rs	74.07% <0.00%> (-3.71%)	⬇️
sctp/src/timer/ack_timer.rs	79.31% <0.00%> (-3.45%)	⬇️
rtp/src/header.rs	62.37% <0.00%> (-1.55%)	⬇️
dtls/src/lib.rs	73.33% <0.00%> (ø)
dtls/src/state.rs	69.56% <0.00%> (ø)
sdp/src/description/session.rs	62.57% <0.00%> (ø)
util/src/vnet/conn/conn_test.rs	53.38% <0.00%> (ø)
ice/src/agent/agent_internal.rs	63.15% <0.00%> (+0.14%)	⬆️
ice/src/agent/agent_gather_test.rs	56.56% <0.00%> (+0.31%)	⬆️

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[k0nserv]

This seems like an improvement, but we have tests on Windows that will run forever due to similar issues. I've stopped the Windows builds to not hog those machines.

I also created an issue to tackle this in other parts of the project.