Add Forgejo forge type constant (#27)

Reviewed-on: https://codeberg.org/woodpecker-plugins/go-plugin/pulls/27
Co-authored-by: Lauris BH <lauris@nix.lv>
Co-committed-by: Lauris BH <lauris@nix.lv>

forge.go

@@ -20,6 +20,7 @@ import (
 
 const (
 	ForgeTypeGitea     = "gitea"
+	ForgeTypeForgejo   = "forgejo"
 	ForgeTypeGitHub    = "github"
 	ForgeTypeGitLab    = "gitlab"
 	ForgeTypeBitbucket = "bitbucket"
@@ -38,7 +39,7 @@ func forgeFlags() []cli.Flag {
 	return []cli.Flag{
 		&cli.StringFlag{
 			Name:  "forge.type",
-			Usage: "forge type (gitea, github, gitlab, bitbucket)",
+			Usage: "forge type (gitea, forgejo, github, gitlab, bitbucket)",
 			EnvVars: []string{
 				"CI_FORGE_TYPE",
 			},