chore: Update SSL check in errors.lua and headers.lua

This commit updates the SSL check in the `errors.lua` and `headers.lua` files to use the `scheme` property of the `bw` context object instead of the `https_configured` property. This change ensures that the SSL check is consistent across the application and follows best practices for secure communication over HTTPS.

src/common/core/errors/errors.lua

@@ -104,7 +104,7 @@ function errors:render_template(code)
 	-- Override HSTS header
 	local ssl
 
-	if self.ctx.bw and self.ctx.bw.https_configured == "yes" then
+	if self.ctx.bw and self.ctx.bw.scheme == "https" then
 		ssl = true
 	else
 		ssl = ngx.var.scheme == "https"

src/common/core/headers/headers.lua

@@ -80,7 +80,7 @@ end
 function headers:header()
 	-- Override upstream headers if needed
 	local ngx_header = ngx.header
-	local ssl = self.ctx.bw.https_configured == "yes"
+	local ssl = self.ctx.bw.scheme == "https"
 	for variable, header in pairs(self.all_headers) do
 		if
 			ngx_header[header] == nil