go/runtime/registry: Refresh key manager policy on runtime changes

[kostko]

Since the runtime can change dynamically (due to version upgrades), we
need to make sure that we notify the new runtime as well.

[codecov]

Codecov Report

Merging #4729 (3f56208) into master (ad8247e) will increase coverage by 0.08%.
The diff coverage is 68.75%.

@@            Coverage Diff             @@
##           master    #4729      +/-   ##
==========================================
+ Coverage   66.77%   66.86%   +0.08%     
==========================================
  Files         440      440              
  Lines       49240    49254      +14     
==========================================
+ Hits        32881    32934      +53     
+ Misses      12287    12280       -7     
+ Partials     4072     4040      -32     

Impacted Files	Coverage Δ
go/runtime/registry/host.go	70.20% <68.75%> (-1.66%)	⬇️
go/consensus/tendermint/apps/staking/auth.go	62.96% <0.00%> (-7.41%)	⬇️
go/runtime/host/sandbox/sandbox.go	59.85% <0.00%> (-6.70%)	⬇️
go/oasis-node/cmd/ias/auth_registry.go	64.10% <0.00%> (-4.28%)	⬇️
go/sentry/api/grpc.go	40.62% <0.00%> (-3.13%)	⬇️
go/common/grpc/grpc.go	79.88% <0.00%> (-2.37%)	⬇️
go/runtime/host/multi/multi.go	72.05% <0.00%> (-1.48%)	⬇️
go/worker/compute/executor/committee/node.go	69.33% <0.00%> (-0.99%)	⬇️
go/registry/api/grpc.go	43.42% <0.00%> (-0.62%)	⬇️
... and 30 more

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