Remove ConflictsWith

Experimentation with `ConflictsWith` for this use case added too much 
friction. This diff opts to use a custom `OwnerOrOrgEnvDefaultFunc` 
function instead to ensure owner and organization flags are used 
correctly in CI.

github/provider.go

@@ -15,18 +15,16 @@ func Provider() terraform.ResourceProvider {
 				Description: descriptions["token"],
 			},
 			"owner": {
-				Type:          schema.TypeString,
-				Optional:      true,
-				DefaultFunc:   schema.EnvDefaultFunc("GITHUB_OWNER", nil),
-				Description:   descriptions["owner"],
-				ConflictsWith: []string{"organization"},
+				Type:        schema.TypeString,
+				Optional:    true,
+				DefaultFunc: OwnerOrOrgEnvDefaultFunc,
+				Description: descriptions["owner"],
 			},
 			"organization": {
-				Type:          schema.TypeString,
-				Optional:      true,
-				DefaultFunc:   schema.EnvDefaultFunc("GITHUB_ORGANIZATION", nil),
-				Description:   descriptions["organization"],
-				ConflictsWith: []string{"owner"},
+				Type:        schema.TypeString,
+				Optional:    true,
+				DefaultFunc: OwnerOrOrgEnvDefaultFunc,
+				Description: descriptions["organization"],
 			},
 			"base_url": {
 				Type:        schema.TypeString,

github/provider_utils.go

@@ -197,3 +197,10 @@ func orgResponseBody(port string) string {
 }
 `, testOwner, url, url)
 }
+
+func OwnerOrOrgEnvDefaultFunc() (interface{}, error) {
+	if organization := os.Getenv("GITHUB_ORGANIZATION"); organization != "" {
+		return os.Getenv("GITHUB_ORGANIZATION"), nil
+	}
+	return os.Getenv("GITHUB_OWNER"), nil
+}