Fix gruvbox diff colors

See:
https://github.com/ellisonleao/gruvbox.nvim/issues/105#issuecomment-1480547367

after/plugin/gruvbox.lua

@@ -0,0 +1,16 @@
+local colors = require("gruvbox.palette").colors;
+
+function FixGruvbox()
+  vim.api.nvim_set_hl(0, 'DiffviewDiffAddAsDelete', { bg = "#431313" })
+  vim.api.nvim_set_hl(0, 'DiffDelete', { bg = "none", fg = colors.dark2 })
+  vim.api.nvim_set_hl(0, 'DiffviewDiffDelete', { bg = "none", fg = colors.dark2 })
+  vim.api.nvim_set_hl(0, 'DiffAdd', { bg = "#142a03" }) -- #122f2f
+  vim.api.nvim_set_hl(0, 'DiffChange', { bg = "#3B3307" })
+  vim.api.nvim_set_hl(0, 'DiffText', { bg = "#4D520D" }) -- #2f3f5c
+end
+FixGruvbox()
+
+vim.api.nvim_create_autocmd(
+  "ColorScheme",
+    { pattern = { "gruvbox" }, callback = FixGruvbox }
+)