fix: handle both build and bake attestation string conversion

Previously, bake would not have the `attest:` prefix but build would.
In upstream the prefix is added late in the process for bake.
This caused builds to add an additional attest: to their prefix.

Signed-off-by: Chris Goller <[email protected]>

Author: goller

pkg/buildx/build/build.go

@@ -401,6 +401,10 @@ func toSolveOpt(ctx context.Context, node builder.Node, multiDriver bool, opt Op
 	supportsAttestations := true
 	if len(attests) > 0 {
 		for k, v := range attests {
+			// DEPOT: Bake does not have `attest:` and build does.
+			if !strings.HasPrefix(k, "attest:") {
+				k = "attest:" + k
+			}
 			so.FrontendAttrs[k] = v
 		}
 	}