codegen: optional-complex-config test is broken

[abhinav]

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Issue details

In upgrading to Pulumi v3.76 (#474), we discovered that the
optional-complex-config test is broken for this repository:

--- FAIL: TestGenerateProgram (0.11s)
    --- FAIL: TestGenerateProgram/optional-complex-config (0.11s)
        gen_program_test.go:217:
                Error Trace:    /Users/abg/src/pulumi/yaml/pkg/pulumiyaml/codegen/gen_program_test.go:217
                                                        /Users/abg/go/pkg/mod/github.com/pulumi/pulumi/pkg/v3@v3.76.1/codegen/testing/test/program_driver.go:635
                Error:          Received unexpected error:
                                1 error occurred:
                                        *
                                -error: ../testing/test/testdata/optional-complex-config-pp/yaml/optional-complex-config.yaml:4,14-18: unknown type;
                                -error: ../testing/test/testdata/optional-complex-config-pp/yaml/optional-complex-config.yaml:7,14-18: unknown type;
                                -error: ../testing/test/testdata/optional-complex-config-pp/yaml/optional-complex-config.yaml:10,14-18: unknown type;
                                -error: ../testing/test/testdata/optional-complex-config-pp/yaml/optional-complex-config.yaml:13,14-18: unknown type;
                                -error: ../testing/test/testdata/optional-complex-config-pp/yaml/optional-complex-config.yaml:16,14-18: unknown type;
                                -error: ../testing/test/testdata/optional-complex-config-pp/yaml/optional-complex-config.yaml:19,14-18: unknown type;

                Test:           TestGenerateProgram/optional-complex-config
FAIL
exit status 1
FAIL    github.com/pulumi/pulumi-yaml/pkg/pulumiyaml/codegen    0.155s

Affected area/feature