Fix bazel build version at 0.22.0 for CI.

[iphydf]

To make this reproducible. With floating versions (always latest), this
can break any time a new bazel version is released.

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This change is 

[codecov]

Codecov Report

Merging #1314 into master will decrease coverage by 0.3%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #1314     +/-   ##
========================================
- Coverage    84.6%   84.2%   -0.4%     
========================================
  Files          85      85             
  Lines       15442   15442             
========================================
- Hits        13078   13017     -61     
- Misses       2364    2425     +61

Impacted Files	Coverage Δ
toxcore/TCP_client.c	62.3% <0%> (-5.2%)	⬇️
toxcore/TCP_server.c	80.3% <0%> (-2.6%)	⬇️
toxav/msi.c	66.4% <0%> (-2%)	⬇️
auto_tests/toxav_basic_test.c	81.6% <0%> (-2%)	⬇️
toxcore/friend_connection.c	94.6% <0%> (-1.5%)	⬇️
toxav/toxav.c	69% <0%> (-1.3%)	⬇️
toxcore/LAN_discovery.c	84.9% <0%> (-1%)	⬇️
toxcore/net_crypto.c	95% <0%> (-0.3%)	⬇️
toxcore/onion_client.c	96.3% <0%> (-0.2%)	⬇️

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