ci: update Go version requirements and remove test files (#3957)

- Update the Go version requirements in `.github/workflows/gin.yml`
- Remove test files for Go versions 1.18 and 1.19
- Update the required Go version in `debug.go` and `debug_test.go`
- Rename and modify files related to Go version 1.19 and 1.20 in the `internal/bytesconv` directory

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

internal/bytesconv/bytesconv.go

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a MIT style
 // license that can be found in the LICENSE file.
 
-//go:build go1.20
-
 package bytesconv
 
 import (

internal/bytesconv/bytesconv_1.19.go

@@ -1,26 +0,0 @@
-// Copyright 2020 Gin Core Team. All rights reserved.
-// Use of this source code is governed by a MIT style
-// license that can be found in the LICENSE file.
-
-//go:build !go1.20
-
-package bytesconv
-
-import (
-	"unsafe"
-)
-
-// StringToBytes converts string to byte slice without a memory allocation.
-func StringToBytes(s string) []byte {
-	return *(*[]byte)(unsafe.Pointer(
-		&struct {
-			string
-			Cap int
-		}{s, len(s)},
-	))
-}
-
-// BytesToString converts byte slice to string without a memory allocation.
-func BytesToString(b []byte) string {
-	return *(*string)(unsafe.Pointer(&b))
-}