fix: set max height for add/replace button (#4085)

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Sets a maxHeight property for add/replace button in playground 
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Signed-off-by: andreas-unleash <andreas@getunleash.ai>

frontend/src/component/playground/Playground/PlaygroundForm/PlaygroundCodeFieldset/PlaygroundCodeFieldset.tsx

@@ -266,7 +266,7 @@ export const PlaygroundCodeFieldset: VFC<IPlaygroundCodeFieldsetProps> = ({
                     variant="outlined"
                     disabled={!contextField || Boolean(error)}
                     onClick={onAddField}
-                    sx={{ width: '95px' }}
+                    sx={{ width: '95px', maxHeight: '40px' }}
                 >
                     {`${!fieldExist ? 'Add' : 'Replace'} `}
                 </Button>