GL: fix a warning in test code in GLES2 builds.

src/Magnum/GL/Test/BufferGLTest.cpp

@@ -79,6 +79,7 @@ struct BufferGLTest: OpenGLTester {
     void invalidate();
 };
 
+#ifndef MAGNUM_TARGET_GLES2
 const struct {
     const char* name;
     bool bindRange;
@@ -99,6 +100,7 @@ const struct {
     {"bind bases", true},
 };
 #endif
+#endif
 
 BufferGLTest::BufferGLTest() {
     addTests({&BufferGLTest::construct,