internal/godebug: check error from os.ReadFile in test

Change-Id: I4770443c8eaa12add2e04cbf9d18ebfbbd851162
Reviewed-on: https://go-review.googlesource.com/c/go/+/643259
Reviewed-by: Michael Pratt <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Commit-Queue: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: ianlancetaylor

src/internal/godebug/godebug_test.go

@@ -109,6 +109,9 @@ func TestCmdBisect(t *testing.T) {
 
 	var want []string
 	src, err := os.ReadFile("godebug_test.go")
+	if err != nil {
+		t.Fatal(err)
+	}
 	for i, line := range strings.Split(string(src), "\n") {
 		if strings.Contains(line, "BISECT"+" "+"BUG") {
 			want = append(want, fmt.Sprintf("godebug_test.go:%d", i+1))