Use own Go version instead of hardcoded 1.17 for make fmt (#21457)

We should make sure we're using the same version across the codebase.
* We upgraded in #19918 but forgot about the following line
https://github.com/go-gitea/gitea/blob/6bb6a108e0c03b323402b452fc05c6845f7d00df/build/code-batch-process.go#L273

Signed-off-by: Yarden Shoham <hrsi88@gmail.com>
Co-authored-by: 6543 <6543@obermui.de>

Author: yardenshoham

build/code-batch-process.go

@@ -206,6 +206,17 @@ Example:
 `, "file-batch-exec")
 }
 
+func getGoVersion() string {
+	goModFile, err := os.ReadFile("go.mod")
+	if err != nil {
+		log.Fatalf(`Faild to read "go.mod": %v`, err)
+		os.Exit(1)
+	}
+	goModVersionRegex := regexp.MustCompile(`go \d+\.\d+`)
+	goModVersionLine := goModVersionRegex.Find(goModFile)
+	return string(goModVersionLine[3:])
+}
+
 func newFileCollectorFromMainOptions(mainOptions map[string]string) (fc *fileCollector, err error) {
 	fileFilter := mainOptions["file-filter"]
 	if fileFilter == "" {
@@ -270,7 +281,7 @@ func main() {
 				log.Print("the -d option is not supported by gitea-fmt")
 			}
 			cmdErrors = append(cmdErrors, giteaFormatGoImports(files, containsString(subArgs, "-l"), containsString(subArgs, "-w")))
-			cmdErrors = append(cmdErrors, passThroughCmd("go", append([]string{"run", os.Getenv("GOFUMPT_PACKAGE"), "-extra", "-lang", "1.17"}, substArgs...)))
+			cmdErrors = append(cmdErrors, passThroughCmd("go", append([]string{"run", os.Getenv("GOFUMPT_PACKAGE"), "-extra", "-lang", getGoVersion()}, substArgs...)))
 		case "misspell":
 			cmdErrors = append(cmdErrors, passThroughCmd("go", append([]string{"run", os.Getenv("MISSPELL_PACKAGE")}, substArgs...)))
 		default: