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>

.github/workflows/gin.yml

@@ -34,7 +34,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        go: ["1.18", "1.19", "1.20", "1.21", "1.22"]
+        go: ["1.20", "1.21", "1.22"]
         test-tags:
           ["", "-tags nomsgpack", '-tags "sonic avx"', "-tags go_json", "-race"]
         include: