Do not adjust logos for viewing in dark mode

[agriyakhetarpal]

The code originating from the PST stylesheets here:

scientific-python-hugo-theme/assets/theme-css/pst/variables/_color.scss

Lines 305 to 320 in 762065e

	/* Adjust images in dark mode (unless they have class .only-dark or
	* .dark-light, in which case assume they're already optimized for dark
	* mode).
	*/
	img:not(.only-dark, .dark-light) {
	filter: brightness(0.8) contrast(1.2);
	}
	/* Give images a light background in dark mode in case they have
	* transparency and black text (unless they have class .only-dark or .dark-light, in
	* which case assume they're already optimized for dark mode).
	*/
	.bd-content img:not(.only-dark, .dark-light) {
	background-color: rgb(255 255 255);
	border-radius: 0.25rem;
	}

unfortunately causes the Scientific Python logo and any custom logos provided by users to appear darker and with increased contrast in dark mode. This PR addresses that issue by adding the dark-light class to all logos to ensure compliance with that rule. I view this as a bug and as an unintended side effect of using these stylesheets, as I believe it would be better for us to leave the decision to adjust logos in dark mode to the respective projects through their own stylesheets.

This is another one of the current dark mode issues; xref #618. Another piece of reasoning behind this: our dark mode support is already pretty sensitive, and we don't want projects' logos to inadvertently break WCAG 1.4.3 when switching to dark mode if their colours are very close to the minimum-contrast threshold!

P.S. I thought about removing this code section from the stylesheets I linked above entirely, but since it's coming from the PST, I decided not to, assuming there must be a reason they included it, and deviating from the PST styles in general warrants a separate discussion elsewhere.

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