Fix for image digest update request

Author: srishtipmishra

CHANGELOG.md

@@ -6,6 +6,9 @@
 - Support for OCI Vulnerability Scanning Service
 - Support for artifacts container image datasource
 
+### Fixed
+- Fixed `image_digest` field update behavior causing issues in `functions` resource
+
 ## 4.19.0 (March 24, 2021)
 
 ### Added

oci/functions_function_resource.go

@@ -282,7 +282,7 @@ func (s *FunctionsFunctionResourceCrud) Update() error {
 		request.Image = &tmp
 	}
 
-	if imageDigest, ok := s.D.GetOkExists("image_digest"); ok {
+	if imageDigest, ok := s.D.GetOkExists("image_digest"); ok && s.D.HasChange("image_digest") {
 		tmp := imageDigest.(string)
 		request.ImageDigest = &tmp
 	}