Update default gitsigns source

lua/plugins/null-ls.lua

@@ -1,13 +1,15 @@
 require("mason").setup()
 require("mason-null-ls").setup({
-    ensure_installed = {
-        -- Opt to list sources here, when available in mason.
-    },
-    automatic_installation = false,
-    handlers = {},
+	ensure_installed = {
+		-- Opt to list sources here, when available in mason.
+	},
+	automatic_installation = false,
+	handlers = {},
 })
-require("null-ls").setup({
-    sources = {
-        -- Anything not supported by mason.
-    }
+
+local null_ls = require("null-ls")
+null_ls.setup({
+	sources = {
+		null_ls.builtins.code_actions.gitsigns,
+	}
 })