Added missing include of cstdint for GCC13

Without the include compilation fails with
```
/opm/io/eclipse/EclFile.hpp:92:17: error: ‘uint64_t’ was not declared in this scope
   92 |     std::vector<uint64_t> ifStreamPos;
      |                 ^~~~~~~~
In file included from src/opm/io/eclipse/EclOutput.cpp:20:
opm/io/eclipse/EclUtil.hpp:56:5: error: 'uint64_t' does not name a type
   56 |     uint64_t sizeOnDiskBinary(int64_t num, Opm::EclIO::eclArrType arrType, int elementSize);
      |     ^~~~~~~~

```

opm/io/eclipse/EclFile.hpp

@@ -28,6 +28,7 @@
 #include <tuple>
 #include <unordered_map>
 #include <vector>
+#include <cstdint>
 
 namespace Opm { namespace EclIO {
 

opm/io/eclipse/EclUtil.hpp

@@ -25,6 +25,7 @@
 #include <tuple>
 #include <vector>
 #include <functional>
+#include <cstdint>
 
 namespace Opm { namespace EclIO {