package/go: adjust Upstream header in patch

Fixes:

  package/go/0002-cmd-dist-set-buildvcs-false-when-building-go-bootstr.patch:0:
  missing Upstream in the header (http://nightly.buildroot.org/#_additional_patch_documentation)

In:

 https://gitlab.com/buildroot.org/buildroot/-/jobs/4763324039

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/go/0002-cmd-dist-set-buildvcs-false-when-building-go-bootstr.patch

@@ -46,7 +46,7 @@ Fixes: https://github.com/golang/go/issues/61620
 
 ---
 
-Upstream PR: https://github.com/golang/go/pull/61621
+Upstream: https://github.com/golang/go/pull/61621
 
 Signed-off-by: Christian Stewart <christian@aperture.us>