Only testPetscBinaryRead with Real==double

They'll only read the format they're configured for, and this test file
was written with type double, not float, not complex<double>, etc.

Author: roystgnr

tests/numerics/petsc_matrix_test.C

@@ -24,8 +24,10 @@ public:
   SPARSEMATRIXTEST
 
   // Our repo's test files use PetscScalar==double
-#ifdef LIBMESH_USE_COMPLEX_NUMBERS
+#ifndef LIBMESH_USE_COMPLEX_NUMBERS
+#ifdef LIBMESH_DEFAULT_DOUBLE_PRECISION
   CPPUNIT_TEST(testPetscBinaryRead);
+#endif
 #endif
 
   CPPUNIT_TEST(testPetscBinaryWrite);