oapi-codegen v2.6.0 fails to compile when used with kin-openapi v0.134.0 due to a type mismatch error.
The code generation step fails with a compilation error in pkg/codegen/schema.go.

Error Message

go generate ./...
# github.com/oapi-codegen/oapi-codegen/v2/pkg/codegen
../../../../go/pkg/mod/github.com/oapi-codegen/oapi-codegen/v2@v2.6.0/pkg/codegen/schema.go:909:13: invalid operation: v == element.Ref (mismatched types openapi3.MappingRef and string)
openapi/oapicodegen.go:8: running "go": exit status 1

Steps to Reproduce

1. Create a project with go.mod that includes:

   require (
       github.com/getkin/kin-openapi v0.134.0
       github.com/oapi-codegen/oapi-codegen/v2 v2.6.0
   )
   tool github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen

2. Create a oapicodegen.go file

   package main
   //go:generate go tool oapi-codegen -config config.yaml spec.yaml

3. Run go generate ./..
4. Observe compilation failure

Expected Behavior

Code generation should complete successfully, as it does with kin-openapi v0.133.0.

Actual Behavior

Compilation fails with type mismatch error. The error suggests that element.Ref changed from type string to openapi3.MappingRef in kin-openapi v0.134.0.

Root Cause

The relevant change in kin-openapi seems to be getkin/kin-openapi@88234d0#diff-e6fbba2cbdca4fd502561d14e4c33ea0080e789c48da5a68814fe196a00dc52aR14-R15

Merge Request: getkin/kin-openapi#1108

Workaround

Downgrade to kin-openapi v0.133.0:

go get github.com/getkin/kin-openapi@v0.133.0
go mod tidy