Do not use fast copy with GL_ALPHA8_EXT

It fixes emulator ANGLE boot with GLES3.

BUG: 64484749
Change-Id: I491aa2d5d27e2f1f9e65e33a81b6b320ffec3f3d
(cherry picked from commit 9f5a49f63a6ae9ca833c74087ffa86ba70112c55)

src/libANGLE/renderer/d3d/d3d11/Renderer11.cpp

diff --git a/src/libANGLE/renderer/d3d/d3d11/Renderer11.cpp b/src/libANGLE/renderer/d3d/d3d11/Renderer11.cpp
index a82c1df..70ee426 100644
--- a/src/libANGLE/renderer/d3d/d3d11/Renderer11.cpp
+++ b/src/libANGLE/renderer/d3d/d3d11/Renderer11.cpp
@@ -3655,6 +3655,13 @@
         return false;
     }
 
+    // This format does not work.
+    // BUG: 64484749
+    if (internalFormat == GL_ALPHA8_EXT)
+    {
+        return false;
+    }
+
     return true;
 }