ci: remove quick-fuzz, guard wasm tests on changed files, limit concurrency (#5030)
ci: remove quick-fuzz, guard wasm tests on changed files, limit concurrency (#5030)

* ci: remove quick-fuzz, guard wasm tests on changed files

This is a first step into running less things all the time that don't need to
be run all the time.

It's a heuristic, and as such fallible: there could always be changes that
break something in the wasm code path, because I have forgotten that there's a
dependency of some sort.

Removing the quick-fuzz target, it's never brought any issues up; and still
runs in nightly tests.

* ci: cancel previous run for PRs

From https://stackoverflow.com/a/72408109/993018.

* ci: avoid rebuilding wasm

Signed-off-by: Stephan Renatus <0d0a21c7604d0d452d5c1019ca18e48a97a9a057@gmail.com>
open-policy-agent/opa,open-policy-agent/opa,open-policy-agent/opa,open-policy-agent/opa,open-policy-agent/opa,open-policy-agent/opa