chore: inject the version into main instead of a module path

The `-X` target carried the full module path in both the Makefile and
.goreleaser.yaml, so any change to the module path silently turned the
injection into a no-op and shipped a binary reporting "dev". Target
`main.version` instead, which no longer names the module, and fail
`make checks` when the injection stops taking effect.

Assisted-by: Codet:GPT-5.1-Codex

internal/pkg/ver/version.go

@@ -3,9 +3,15 @@
 
 package ver
 
-// go build -ldflags "-X gitea.com/gitea/runner/internal/pkg/ver.version=1.2.3"
 var version = "dev"
 
+// SetVersion records the version injected into package main at build time.
+func SetVersion(v string) {
+	if v != "" {
+		version = v
+	}
+}
+
 func Version() string {
 	return version
 }