fix: use `auto` for the database selector width (#802)

Signed-off-by: ryjiang <jiangruiyi@gmail.com>

client/src/components/layout/Header.tsx

@@ -71,7 +71,7 @@ const Title = styled(Typography)(({ theme }) => ({
 
 const DatabaseSelector = styled(CustomSelector)(({ theme }) => ({
   transform: 'translateY(-4px)',
-  width: theme.spacing(16),
+  width: 'auto',
   '& .MuiInputLabel-root': {
     top: '4px',
   },