build: terminate long running tests (#6389)

configures nextest to kill tests after 1 minute. slow period is set to
20s which is how long our tests currently take in total, there will be 2
warnings and then the test will be killed and it's output logged.

Cc: #6361
Cc: #6368 -- likely this will be enough for longer time, but it will be
counter productive when we want to attach and debug; the added line
would have to be commented out.

.config/nextest.toml

@@ -1,2 +1,2 @@
 [profile.default]
-slow-timeout = "1m"
+slow-timeout = { period = "20s", terminate-after = 3 }