Excavator: Run go fix to apply Go 1.26+ modernizers

githubapp/client_creator.go

@@ -399,7 +399,7 @@ func noStoreServerErrors(next http.RoundTripper) http.RoundTripper {
 			// Preserve existing Cache-Control directives.
 			cacheControl := resp.Header.Get("Cache-Control")
 			// Don't add a no-store directive if it already exists.
-			for _, directive := range strings.Split(cacheControl, ",") {
+			for directive := range strings.SplitSeq(cacheControl, ",") {
 				if strings.TrimSpace(directive) == "no-store" {
 					return resp, err
 				}

githubapp/client_creator_test.go

@@ -16,6 +16,7 @@ package githubapp
 
 import (
 	"io"
+	"maps"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -121,9 +122,7 @@ type cacheTestResponse struct {
 
 func newCacheTestResponse(status int, header http.Header) *http.Response {
 	recorder := httptest.NewRecorder()
-	for key, values := range header {
-		recorder.Header()[key] = values
-	}
+	maps.Copy(recorder.Header(), header)
 	recorder.WriteHeader(status)
 	return recorder.Result()
 }