test/integration/install: stub languageserver restart command

gopls restart command is called and creates a promise after gopls
installation.
Skip calling the command by stubbing the command call during
installation testing.

Fixes #2356

Change-Id: I9350d18b86f2a4f306909a7159eb291602648d41
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/418548
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Suzy Mueller <suzmue@golang.org>

Author: hyangah

test/integration/install.test.ts

@@ -104,6 +104,9 @@ suite('Installation Tests', function () {
 
 		const missingTools = testCases.map((tc) => getToolAtVersion(tc.name));
 		const goVersion = await getGoVersion();
+
+		sandbox.stub(vscode.commands, 'executeCommand').withArgs('go.languageserver.restart');
+
 		await installTools(missingTools, goVersion);
 
 		// Confirm that each expected tool has been installed.