Fix gridline labels ignoring side visibility on curved projections

[guillermodotn]

Rationale

On non-rectangular projections (e.g. Robinson), gridline labels on the curved boundary get classified as "geo" instead of a named side, bypassing right_labels=False (or equivalent).

For example, 60°N and 60°S still appear on the right even when gl.right_labels = False.

Closes #2607

After fix sample:

Implications

• Single condition expanded in _draw_gridliner: when a label's loc is "geo", also check the angle-derived side attribute. Uses is False to avoid changing default behavior for users who haven't explicitly disabled a side.
• No additional tests added.

[CLAassistant]

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[adrifoster]

Is there a way to fix this without having to update the version once this comes in? I'm trying to plot something and I am having trouble getting the 60N and 60S to disappear:

    fig, axes = plt.subplots(nrows, ncols, figsize=(width, height),
                            subplot_kw=dict(projection=ccrs.Robinson()),
                            layout="compressed")
                            
    for i, da in enumerate(das):

        map_function(axes[i], da, titles[i], cmap=cmap, vmin=-0.5, vmax=len(cols)-0.5)
        
        gls = axes[i].gridlines(draw_labels=True, dms=True, x_inline=False,
                          y_inline=False)
        gls.top_labels = False
        gls.right_labels = False
        
        if i%ncols > 0:
            gls.left_labels = False
        if i < (len(axes) - ncols):
            gls.bottom_labels = False
    
        gls.ylocator = FixedLocator([-60, -30, 0, 30, 60])
        gls.xlabel_style = {'size': 10}
        gls.ylabel_style = {'size': 10}
        axes[i].set_extent([-180, 180, -60, 89], crs=ccrs.PlateCarree())
        
        ```