Excess padding in nav bar dropdown

[gabalafou]

      .dropdown-menu {
        z-index: $zindex-popover;
        border: 1px solid var(--pst-color-border);
        box-shadow: 0 0 0.3rem 0.1rem var(--pst-color-shadow);
        background-color: var(--pst-color-on-background);
        padding: 0.5rem 0;

IMO we don't need the top/bottom padding either, but feel free to ignore this suggestion if you disagree

        padding: 0;

Originally posted by @drammock in https://github.com/pydata/pydata-sphinx-theme/pull/1414#discussion_r1297758428