chore: bump minimum go version to 1.22

Author: stainless-app[bot]

go.mod

@@ -1,6 +1,6 @@
 module github.com/stainless-api/stainless-api-go
 
-go 1.21
+go 1.22
 
 require (
 	github.com/tidwall/gjson v1.14.4

internal/encoding/json/shims/shims.go

@@ -1,5 +1,5 @@
 // This package provides shims over Go 1.2{2,3} APIs
-// which are missing from Go 1.21, and used by the Go 1.24 encoding/json package.
+// which are missing from Go 1.22, and used by the Go 1.24 encoding/json package.
 //
 // Inside the vendored package, all shim code has comments that begin look like
 // // SHIM(...): ...