Bump to Fable 4.27 and adjust ifdef for Fable4

Author: wallymathieu

.config/dotnet-tools.json

@@ -3,7 +3,7 @@
   "isRoot": true,
   "tools": {
     "fable": {
-      "version": "4.23.0",
+      "version": "4.27.0",
       "commands": [
         "fable"
       ]

src/FSharpPlus/Control/Comonad.fs

@@ -7,7 +7,7 @@ open System.Threading.Tasks
 open FSharpPlus
 open FSharpPlus.Extensions
 open FSharpPlus.Internals
-#if !FABLE_COMPILER4
+#if !FABLE_COMPILER_4
 
 // Comonad class ----------------------------------------------------------