Tests: Fix Fortran syntax for initialized variable

LFortran 0.44 errors without the `::`.

Tests/FortranOnly/preprocess2.f

@@ -1,6 +1,6 @@
 #define int INTEGER
        ! This single unmatched quote ' should not cause an error during compilation
        PROGRAM PREPRO
-       int f = 1
+       int :: f = 1
        PRINT*, f
        END