[BUG] [Golang] unexported name is generated for enum

Description

When I generate Go model code for an enum where a value starts with a number then the generated const will be unexported.

Actual:
// List of AccessType
const (
_3_GPP_ACCESS AccessType = "3GPP_ACCESS"
NON_3_GPP_ACCESS AccessType = "NON_3GPP_ACCESS"
)

Expected e.g.:
// List of AccessType
const (
ACCESS_TYPE_3_GPP_ACCESS AccessType = "3GPP_ACCESS"
ACCESS_TYPE_NON_3_GPP_ACCESS AccessType = "NON_3GPP_ACCESS"
)

Input validation:

docker run --rm -it -w /gen -e GEN_DIR=/gen -e MAVEN_CONFIG=/var/maven/.m2 -u 0:0 -v /ephemeral/opentas/openapi-generator:/gen -v /root/.m2:/root/.m2 --entrypoint /gen/docker-entrypoint.sh maven:3-jdk-8 validate -i 5GC_APIs/TS29122_CommonData.yaml
Validating spec (5GC_APIs/TS29122_CommonData.yaml)
No validation issues detected.

docker run --rm -it -w /gen -e GEN_DIR=/gen -e MAVEN_CONFIG=/var/maven/.m2 -u 0:0 -v /ephemeral/opentas/openapi-generator:/gen -v /root/.m2:/root/.m2 --entrypoint /gen/docker-entrypoint.sh maven:3-jdk-8 validate -i 5GC_APIs/TS29518_Namf_MT.yaml
Validating spec (5GC_APIs/TS29518_Namf_MT.yaml)
No validation issues detected.

openapi-generator version

4.0.0-SNAPSHOT

OpenAPI declaration file content or url

Type:
https://github.com/jdegre/5GC_APIs/blob/7298845c7ede07038838d5c40debb083f929f98b/TS29571_CommonData.yaml#L537

**AccessType:
  type: string
  enum:
    - 3GPP_ACCESS
    - NON_3GPP_ACCESS**

Service:
https://github.com/jdegre/5GC_APIs/blob/78b04e48a7fb92b1a5dc6f95419c9ed2f6c3c5ed/TS29518_Namf_MT.yaml#L164

Command line used for generation

./run-in-docker.sh generate -i 5GC_APIs/TS29518_Namf_MT.yam -g go -o /gen/out -Dmodels

Steps to reproduce

./run-in-docker.sh generate -i 5GC_APIs/TS29518_Namf_MT.yam -g go -o /gen/out -Dmodels
cat out/model_access_type.go

Reproduce the issue with the listed run-in-docker.sh generate command and inspect out/model_access_type.go for the AccessType enum. Trace the Go generator path that derives names from enum values beginning with a number, then confirm the generated constants are exported and retain the expected string values.