cmd/gitops-pusher: default previousEtag to controlEtag (#14296)

If previousEtag is empty, then we assume control ACLs were not modified
manually and push the local ACLs. Instead, we defaulted to localEtag
which would be different if local ACLs were different from control.

AFAIK this was always buggy, but never reported?

Fixes #14295

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

cmd/gitops-pusher/gitops-pusher.go

@@ -58,8 +58,8 @@ func apply(cache *Cache, client *http.Client, tailnet, apiKey string) func(conte
 		}
 
 		if cache.PrevETag == "" {
-			log.Println("no previous etag found, assuming local file is correct and recording that")
-			cache.PrevETag = localEtag
+			log.Println("no previous etag found, assuming the latest control etag")
+			cache.PrevETag = controlEtag
 		}
 
 		log.Printf("control: %s", controlEtag)
@@ -105,8 +105,8 @@ func test(cache *Cache, client *http.Client, tailnet, apiKey string) func(contex
 		}
 
 		if cache.PrevETag == "" {
-			log.Println("no previous etag found, assuming local file is correct and recording that")
-			cache.PrevETag = localEtag
+			log.Println("no previous etag found, assuming the latest control etag")
+			cache.PrevETag = controlEtag
 		}
 
 		log.Printf("control: %s", controlEtag)
@@ -148,8 +148,8 @@ func getChecksums(cache *Cache, client *http.Client, tailnet, apiKey string) fun
 		}
 
 		if cache.PrevETag == "" {
-			log.Println("no previous etag found, assuming local file is correct and recording that")
-			cache.PrevETag = Shuck(localEtag)
+			log.Println("no previous etag found, assuming control etag")
+			cache.PrevETag = Shuck(controlEtag)
 		}
 
 		log.Printf("control: %s", controlEtag)