Fix language inclusivity for SurfaceMtl.mm

He->they

Bug: b/162834212
Change-Id: I8559120ad77006aaa839b70e00b4c8f12e9e8a44
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2364192
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>

src/libANGLE/renderer/metal/SurfaceMtl.mm

@@ -112,7 +112,7 @@ bool IsFrameCaptureEnabled()
 #else
     // We only support frame capture programmatically if the ANGLE_METAL_FRAME_CAPTURE
     // environment flag is set. Otherwise, it will slow down the rendering. This allows user to
-    // finely control whether he wants to capture the frame for particular application or not.
+    // finely control whether they want to capture the frame for particular application or not.
     auto var                  = std::getenv("ANGLE_METAL_FRAME_CAPTURE");
     static const bool enabled = var ? (strcmp(var, "1") == 0) : false;