update buildkit to 0.19.0 and buildx to 0.20.1

[crazy-max]

No description provided.

[crazy-max]

https://github.com/docker/actions-toolkit/actions/runs/12888049135/job/35932056137?pr=572#step:2:3060

#26 74.99 FAIL __tests__/buildx/bake.test.ts
#26 74.99   ● getDefinition › given ["/src/__tests__/.fixtures/bake-03.hcl"]
#26 74.99 
#26 74.99     expect(received).toEqual(expected) // deep equality
#26 74.99 
#26 74.99     - Expected  - 1
#26 74.99     + Received  + 0
#26 74.99 
#26 74.99     @@ -8,11 +8,10 @@
#26 74.99         },
#26 74.99         "target": Object {
#26 74.99           "default": Object {
#26 74.99             "attest": Array [
#26 74.99               Object {
#26 74.99     -           "mode": "max",
#26 74.99                 "type": "provenance",
#26 74.99               },
#26 74.99               Object {
#26 74.99                 "disabled": true,
#26 74.99                 "type": "sbom",
#26 74.99 
#26 74.99       110 |       targets: targets,
#26 74.99       111 |       overrides: overrides
#26 74.99     > 112 |     }, execOptions)).toEqual(expectedDef);
#26 74.99           |                      ^
#26 74.99       113 |   }, 30 * 60 * 1000);
#26 74.99       114 | });
#26 74.99       115 |
#26 74.99 
#26 74.99       at __tests__/buildx/bake.test.ts:112:22
#26 74.99       at fulfilled (__tests__/buildx/bake.test.ts:43:58)

needs docker/buildx#2936