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>

context_test.go

@@ -90,6 +90,19 @@ func TestContextFormFile(t *testing.T) {
 	assert.NoError(t, c.SaveUploadedFile(f, "test"))
 }
 
+func TestContextFormFileFailed(t *testing.T) {
+	buf := new(bytes.Buffer)
+	mw := multipart.NewWriter(buf)
+	mw.Close()
+	c, _ := CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest("POST", "/", nil)
+	c.Request.Header.Set("Content-Type", mw.FormDataContentType())
+	c.engine.MaxMultipartMemory = 8 << 20
+	f, err := c.FormFile("file")
+	assert.Error(t, err)
+	assert.Nil(t, f)
+}
+
 func TestContextMultipartForm(t *testing.T) {
 	buf := new(bytes.Buffer)
 	mw := multipart.NewWriter(buf)