Move GITHUB_PASSWORD env var check out of VersionRepoUpdater.

build_projects/shared-build-targets-utils/Utils/EnvVars.cs

@@ -1,4 +1,5 @@
 using System;
+using Microsoft.DotNet.Cli.Build.Framework;
 
 namespace Microsoft.DotNet.Cli.Build
 {
@@ -28,5 +29,16 @@ namespace Microsoft.DotNet.Cli.Build
                     return defaultValue;
             }
         }
+
+        public static string EnsureVariable(string variableName)
+        {
+            string value = Environment.GetEnvironmentVariable(variableName);
+            if (string.IsNullOrEmpty(value))
+            {
+                throw new BuildFailureException($"'{variableName}' environment variable was not found.");
+            }
+
+            return value;
+        }
     }
 }