fix ci warning (#3691)

doc/user_guide/transform/pivot.rst

@@ -43,18 +43,18 @@ values on multiple lines:
 
 .. altair-plot::
 
-    import altair as alt
-    from vega_datasets import data
+   import altair as alt
+   from vega_datasets import data
 
-    source = data.stocks()
-    base = alt.Chart(source).encode(x='date:T')
-    columns = sorted(source.symbol.unique())
-    selection = alt.selection_point(
-        fields=['date'], nearest=True, on='pointerover', empty=False, clear='pointerout'
-    )
+   source = data.stocks()
+   base = alt.Chart(source).encode(x='date:T')
+   columns = sorted(source.symbol.unique())
+   selection = alt.selection_point(
+       fields=['date'], nearest=True, on='pointerover', empty=False, clear='pointerout'
+   )
 
-    lines = base.mark_line().encode(y='price:Q', color='symbol:N')
-    points = lines.mark_point().transform_filter(selection)
+   lines = base.mark_line().encode(y='price:Q', color='symbol:N')
+   points = lines.mark_point().transform_filter(selection)
 
    rule = base.transform_pivot(
        'symbol', value='price', groupby=['date']
@@ -63,7 +63,7 @@ values on multiple lines:
        tooltip=[alt.Tooltip(c, type='quantitative') for c in columns]
    ).add_params(selection)
 
-    lines + points + rule
+   lines + points + rule
 
 
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