testing: fix layout issues for long test labels (microsoft#153838)

Fixes microsoft#152959
Fixes microsoft#152622

Some regressions caused by a PR (adding pre-wrap in an attempt to space icons). Instead use flex gap, and fixup sizing for the actions

Author: connor4312

src/vs/workbench/contrib/testing/browser/media/testing.css

@@ -19,10 +19,11 @@
 .test-output-peek-tree .test-peek-item .name {
 	display: flex;
 	align-items: center;
-}
-
-.test-explorer .test-item .label {
-	white-space: pre-wrap;
+	flex-grow: 1;
+	gap: 0.15em;
+	width: 0;
+	overflow: hidden;
+	white-space: nowrap;
 }
 
 .test-explorer .test-item,