Revert "Remove unused includes"

This reverts commit 005d1a0.

Author: emmatyping

Modules/_zstd/compressor.c

@@ -17,6 +17,7 @@ class _zstd.ZstdCompressor "ZstdCompressor *" "&zstd_compressor_type_spec"
 #include "_zstdmodule.h"
 #include "buffer.h"
 #include "zstddict.h"
+#include "internal/pycore_lock.h" // PyMutex_IsLocked
 
 #include <stddef.h>               // offsetof()
 #include <zstd.h>                 // ZSTD_*()

Modules/_zstd/decompressor.c

@@ -17,6 +17,7 @@ class _zstd.ZstdDecompressor "ZstdDecompressor *" "&zstd_decompressor_type_spec"
 #include "_zstdmodule.h"
 #include "buffer.h"
 #include "zstddict.h"
+#include "internal/pycore_lock.h" // PyMutex_IsLocked
 
 #include <stdbool.h>              // bool
 #include <stddef.h>               // offsetof()