extension/src/goTest: save only dirty files

Fixes #3837

Change-Id: I46bbd7d3c4dea866bff2419a631f2407d6989835
GitHub-Last-Rev: 2d7676b
GitHub-Pull-Request: #3838
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/696355
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Hongxiang Jiang <hxjiang@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>

Author: tamayika

extension/src/goTest/run.ts

@@ -247,7 +247,9 @@ export class GoTestRunner {
 		// Save all documents that contain a test we're about to run, to ensure `go
 		// test` has the latest changes
 		const fileUris = new Set(Array.from(files).map((x) => x.uri));
-		await Promise.all(this.workspace.textDocuments.filter((x) => fileUris.has(x.uri)).map((x) => x.save()));
+		await Promise.all(
+			this.workspace.textDocuments.filter((x) => fileUris.has(x.uri) && x.isDirty).map((x) => x.save())
+		);
 
 		let hasBench = false,
 			hasNonBench = false;