ferra: fix ruler overriding foreground style

Ferra's current ruler styling overrides the foreground style, which is
an odd look only for characters in the ruler column. This commit removes
the foreground styling for the ruler rule, which is more in line with
what other themes do.

runtime/themes/ferra.toml

@@ -52,7 +52,7 @@
 "ui.selection.primary" = { bg = "ferra_night", fg = "ferra_umber" }
 "ui.virtual" = { fg = "ferra_bark" }
 "ui.virtual.whitespace" = { fg = "ferra_bark" }
-"ui.virtual.ruler" = { fg = "ferra_night", bg = "ferra_ash" }
+"ui.virtual.ruler" = { bg = "ferra_ash" }
 "ui.virtual.indent-guide" = { fg = "ferra_ash" }
 "ui.virtual.inlay-hint" = { fg = "ferra_bark" }