Start of branch 3.4.x, adapt CI and build (reactor#2928)

The newly branched out 3.4.x now contains development
work for 2020.0 train, 3.4.16-SNAPSHOT version.

Adapt CI workflows and build for this new branch.

.github/workflows/publish.yml

@@ -3,6 +3,7 @@ on:
   push:
     branches: # For branches, better to list them explicitly than regexp include
       - main
+      - 3.4.x
       - 3.3.x
 permissions: read-all
 jobs:

build.gradle

@@ -118,7 +118,7 @@ spotless {
 		enforceCheck false
 	}
 	else {
-		String spotlessBranch = "origin/main"
+		String spotlessBranch = "origin/3.4.x"
 		println "[Spotless] Local run detected, ratchet from $spotlessBranch"
 		ratchetFrom spotlessBranch
 	}