internal/lsp: delay longer in TestDebouncer

Amazingly the builders are occasionally so slow that they can't send the
next event within 100ms. Debounce longer to give them a bit more time.

Change-Id: Ib06bef77099c569060dd32c5b964bf394103485a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/266698
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Robert Findley <rfindley@google.com>

internal/lsp/debounce_test.go

@@ -63,7 +63,7 @@ func TestDebouncer(t *testing.T) {
 			for i, e := range test.events {
 				wg.Add(1)
 				go func(e *event) {
-					d.debounce(e.key, e.order, 100*time.Millisecond, func() {
+					d.debounce(e.key, e.order, 500*time.Millisecond, func() {
 						e.fired = true
 					})
 					wg.Done()