cmd/govulncheck: fix build error from CL 437786

Fix:

cmd/govulncheck/main.go:81:21: cannot use packages.Config{…} (value of
type packages.Config) as type *packages.Config in struct literal

Change-Id: Ibf47f5a4a079a87bfc4f8031bf48362a6b5512bb
Reviewed-on: https://go-review.googlesource.com/c/vuln/+/437862
Run-TryBot: Julie Qiu <julieqiu@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>
diff --git a/cmd/govulncheck/main.go b/cmd/govulncheck/main.go
index 37d27ea..f4bfadf 100644
--- a/cmd/govulncheck/main.go
+++ b/cmd/govulncheck/main.go
@@ -80,7 +80,7 @@
 		AnalysisType: mode,
 		OutputType:   outputType,
 		Patterns:     patterns,
-		SourceLoadConfig: packages.Config{
+		SourceLoadConfig: &packages.Config{
 			Dir:        filepath.FromSlash(dirFlag),
 			Tests:      *testFlag,
 			BuildFlags: buildFlags,