Fix existing issue search

Only search for token, not whole body. Tested running locally.

upgrade/steps_helpers.go

@@ -672,6 +672,7 @@ var getExpectedTargetFromIssues = stepv2.Func11E("From Issues", func(ctx context
 })
 
 // Hide searchable token in the issue body via an HTML comment to help us find this issue later without requiring labels to be set up.
+const upgradeIssueToken = "pulumiupgradeproviderissue"
 const upgradeIssueBodyTemplate = `
 <!-- for upgrade-provider issue searching: pulumiupgradeproviderissue -->
 
@@ -723,7 +724,7 @@ func upgradeIssueExits(ctx context.Context, title, repoOrg, repoName string) (bo
 	// Search through existing pulumiupgradeproviderissue issues to see if we've already created one for this version.
 	issues, err := searchIssues(ctx,
 		fmt.Sprintf("--repo=%s", repoOrg+"/"+repoName),
-		fmt.Sprintf("--search=%q", upgradeIssueBodyTemplate),
+		fmt.Sprintf("--search=%q", upgradeIssueToken),
 		"--state=open")
 	if err != nil {
 		return false, err