Update jsonfieldname linter to support $ in json tag names

.golangci.yml

@@ -202,7 +202,6 @@ linters:
             - RepositoriesSearchResult.Repositories
             - RepositoriesSearchResult.Total
             - RepositoryVulnerabilityAlert.GitHubSecurityAdvisoryID
-            - SCIMDisplayReference.Ref
             - SecretScanningAlertLocationDetails.Startline # TODO: StartLine
             - SecretScanningPatternOverride.Bypassrate # TODO: BypassRate
             - StarredRepository.Repository # TODO: Repo

tools/jsonfieldname/jsonfieldname.go

@@ -134,6 +134,8 @@ func checkGoFieldName(structName, goFieldName, jsonTagName string, tokenPos toke
 }
 
 func splitJSONTag(jsonTagName string) []string {
+	jsonTagName = strings.TrimPrefix(jsonTagName, "$")
+
 	if strings.Contains(jsonTagName, "_") {
 		return strings.Split(jsonTagName, "_")
 	}

tools/jsonfieldname/testdata/src/has-warnings/main.go

@@ -10,4 +10,5 @@ type Example struct {
 	Id               string `json:"id,omitempty"`               // want `change Go field name "Id" to "ID" for JSON tag "id" in struct "Example"`
 	strings          string `json:"strings,omitempty"`          // want `change Go field name "strings" to "Strings" for JSON tag "strings" in struct "Example"`
 	camelcaseexample *int   `json:"camelCaseExample,omitempty"` // want `change Go field name "camelcaseexample" to "CamelCaseExample" for JSON tag "camelCaseExample" in struct "Example"`
+	DollarRef        string `json:"$ref"`                       // want `change Go field name "DollarRef" to "Ref" for JSON tag "\$ref" in struct "Example"`
 }

tools/jsonfieldname/testdata/src/no-warnings/main.go

@@ -9,4 +9,5 @@ type Example struct {
 	GithubThing string `json:"github_thing"`      // Should not be flagged
 	ID          string `json:"id,omitempty"`      // Should not be flagged
 	Strings     string `json:"strings,omitempty"` // Should not be flagged
+	Ref         string `json:"$ref,omitempty"`    // Should not be flagged
 }