Fail CI when tests are logging (#2748)

A re-iteration of a miserable attempt from #2694

Hi @dgvncsz0f, how you've been ;D

.github/bin/log-watch.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+fail=false
+while read l
+do
+  echo "$l"
+  if echo "$l" | grep -qP '\[(warning|error)\]'
+  then 
+    fail=true; 
+  fi
+done
+
+if [ $fail = true ]
+then
+  echo
+  echo "💀 The tests are logging, please capture logs. See:"
+  echo "  - https://hexdocs.pm/ex_unit/1.12/ExUnit.CaptureLog.html"
+  echo "  - https://hexdocs.pm/ex_unit/1.12/ExUnit.Case.html#module-known-tags"
+  echo
+  exit 1
+fi

.github/workflows/elixir.yml

@@ -71,7 +71,7 @@ jobs:
       - name: Check Credo Warnings
         run: mix credo diff --from-git-merge-base origin/master
       - name: Run tests
-        run: mix test --include slow --max-failures 1 --warnings-as-errors
+        run: mix test --include slow --max-failures 1 --warnings-as-errors | .github/bin/log-watch.sh
       - name: Check Dialyzer
         run: mix dialyzer
 env: