refactor: refactor HTTP request handling and improve linter settings

- Remove the `exportloopref` linter from the golangci configuration
- Add the `strconv` package import in `main.go`
- Replace the `fmt.Sprintf` for the year with `strconv.Itoa` to convert the year to a string
- Update the HTTP request method to use `http.MethodPost` instead of a string literal in `plugin.go`

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

plugin.go

@@ -163,7 +163,7 @@ func newfileUploadRequest(uri string, params map[string]string, paramName, path
 		return nil, err
 	}
 
-	req, err := http.NewRequest("POST", uri, body)
+	req, err := http.NewRequest(http.MethodPost, uri, body)
 	req.Header.Set("Content-Type", writer.FormDataContentType())
 	return req, err
 }