Add go.mod replace for go-cty and update the Packer SDK

[optik-aper]

Description

Following the workaround in issue #262

go test -v . ./builder/vultr -timeout 60m                                                                                                                                                                  1 ↵ 15:56
?       github.com/vultr/packer-plugin-vultr    [no test files]
=== RUN   TestArtifact_Impl
--- PASS: TestArtifact_Impl (0.00s)
=== RUN   TestArtifactId
--- PASS: TestArtifactId (0.00s)
=== RUN   TestArtifactString
--- PASS: TestArtifactString (0.00s)
=== RUN   TestBuilderAcc
    builder_acc_test.go:60: Acceptance tests skipped unless env 'PACKER_ACC' set
--- SKIP: TestBuilderAcc (0.00s)
=== RUN   TestBuilder_ImplementsBuilder
--- PASS: TestBuilder_ImplementsBuilder (0.00s)
=== RUN   TestBuilder_Prepare_BadType
--- PASS: TestBuilder_Prepare_BadType (0.00s)
=== RUN   TestBuilderPrepare_InvalidKey
--- PASS: TestBuilderPrepare_InvalidKey (0.00s)
=== RUN   TestBuilderPrepare_RegionID
--- PASS: TestBuilderPrepare_RegionID (0.00s)
=== RUN   TestBuilderPrepare_OSID
--- PASS: TestBuilderPrepare_OSID (0.00s)
=== RUN   TestBuilderPrepare_PlanID
--- PASS: TestBuilderPrepare_PlanID (0.00s)
=== RUN   TestBuilderPrepare_Description
--- PASS: TestBuilderPrepare_Description (0.00s)
=== RUN   TestBuilderPrepare_StateTimeout
--- PASS: TestBuilderPrepare_StateTimeout (0.00s)
=== RUN   TestBuilderPrepare_EnablePrivateNetwork
--- PASS: TestBuilderPrepare_EnablePrivateNetwork (0.00s)
=== RUN   TestBuilderPrepare_EnableIPV6
--- PASS: TestBuilderPrepare_EnableIPV6 (0.00s)
=== RUN   TestBuilderPrepare_Label
--- PASS: TestBuilderPrepare_Label (0.00s)
PASS
ok      github.com/vultr/packer-plugin-vultr/builder/vultr      0.016s

Related Issues

closes #262

Checklist:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you linted your code locally prior to submission?
• Have you successfully ran tests with your changes locally?