ORC-1871: Include iomanip at Test(DictionaryEncoding|ConvertColumnReader)

### What changes were proposed in this pull request?

Add missing includes in source files

### Why are the changes needed?

To package `orc` in The Linux NixOS distribution. The [PR](NixOS/nixpkgs#395541) has already be merged, it will be available to the public very soon ([PR tracker](https://nixpkgs-tracker.ocfox.me/?pr=395541)). This is [the commit](NixOS/nixpkgs@48ff182) to add `apache-orc` to NixOS in a **reproducible way**.

### How was this patch tested?

Compilation is now successfully achieved with the patch.

### Was this patch authored or co-authored using generative AI tooling?

Absolutely not.

Closes #2175 from drupol/push-yvkkqmxxmzxl.

Authored-by: Pol Dellaiera <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: drupol

c++/test/TestConvertColumnReader.cc

@@ -27,6 +27,7 @@
 #include "ConvertColumnReader.hh"
 #include "MemoryInputStream.hh"
 #include "MemoryOutputStream.hh"
+#include <iomanip>
 
 namespace orc {
 

c++/test/TestDictionaryEncoding.cc

@@ -25,6 +25,7 @@
 #include "wrap/gtest-wrapper.h"
 
 #include <cmath>
+#include <iomanip>
 #include <sstream>
 
 namespace orc {