bake: fix attest disabled attribute

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

__tests__/.fixtures/bake-03-default.json

@@ -9,7 +9,7 @@
           "type": "provenance"
         },
         {
-          "disabled": "true",
+          "disabled": true,
           "type": "sbom"
         }
       ],

src/buildx/bake.ts

@@ -238,6 +238,9 @@ export class Bake {
         case 'type':
           attestEntry.type = value;
           break;
+        case 'disabled':
+          attestEntry.disabled = Util.parseBool(value);
+          break;
         default:
           attestEntry[key] = value;
       }

src/types/buildx/bake.ts

@@ -52,7 +52,8 @@ export interface Target {
 
 export interface AttestEntry {
   type: string;
-  [key: string]: string;
+  disabled?: string | boolean;
+  [key: string]: string | boolean | undefined;
 }
 
 export interface CacheEntry {