Frontend.XF.GTK: fix currency colors on GTK #3247

Job	Run time
linux-github--dotnet-and-newmono	6m 32s
linux-github--dotnet-and-mono	3m 37s
linux-vanilla--stockdotnet6-and-newmono	5m 28s
linux-vanilla--stockdotnet6-and-stockmono	6m 21s
linux-vanilla--stockdotnet6-only	4m 51s
linux-vanilla--stockmono-only	4m 47s
linux-vanilla--newmono-only	7m 37s
macOS--dotnet6-and-mono	11m 57s
macOS--dotnet6-only	3m 52s
macOS--mono-only	10m 43s
windows--dotnet6-and-legacyFramework	5m 58s
windows--dotnet6-only	6m 16s
windows--legacyFramework-only	14m 26s
conventions	1m 12s
snap_pkg	6m 45s
snap_pkg_beta	6m 33s
	1h 46m 55s

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