Use COVERALLS environment variable to detect when coveralls is required

.github/workflows/ci.yml

@@ -35,7 +35,7 @@ jobs:
       env:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       run: |
-        rebar3 as test coveralls send
+        COVERALLS=true rebar3 as test coveralls send
         curl -v -k https://coveralls.io/webhook \
              --header "Content-Type: application/json" \
              --data '{"repo_name":"$GITHUB_REPOSITORY",

rebar.config.script

@@ -119,7 +119,7 @@ Rules = [
 			     {compile, {pc, compile}},
 			     {clean, {pc, clean}}
 			    ]}]), []},
-	 {[plugins], IsRebar3 and (os:getenv("GITHUB_ACTIONS") == "true"),
+	 {[plugins], os:getenv("COVERALLS") == "true",
 	  AppendList([{coveralls, {git,
 	                           "https://github.com/RoadRunnr/coveralls-erl.git",
 	                           {branch, "feature/git-info"}}} ]), []},