updatecli: use GITHUB_ACTOR instead (#5426)

Author: v1v

.ci/updatecli/updatecli-bump-golang.yml

@@ -52,7 +52,7 @@ sources:
       owner: golang
       repository: go
       token: '{{ requiredEnv "GITHUB_TOKEN" }}'
-      username: '{{ requiredEnv "GIT_USER" }}'
+      username: '{{ requiredEnv "GITHUB_ACTOR" }}'
       versionfilter:
         kind: regex
         pattern: go1\.{{ source "minor" }}\.(\d*)$