Bugfix/fix meta getitem

Fixes arosics#88 (closed) and improves coverage of GDAL_Metadata class.

HISTORY.rst

@@ -2,6 +2,13 @@
 History
 =======
 
+0.17.3 (coming soon)
+--------------------
+
+* !47: Fixed missing handling of int64 input values for GDAL_Metadata.__getitem__
+  and improved coverage of GDAL_Metadata.
+
+
 0.17.2 (23.11.2023)
 -------------------