Document the supported TLS versions in HTTPRequest

See godotengine#42857.

(cherry picked from commit 0ebbc76)

doc/classes/HTTPClient.xml

@@ -9,6 +9,7 @@
 		A [HTTPClient] should be reused between multiple requests or to connect to different hosts instead of creating one client per request. Supports SSL and SSL server certificate verification. HTTP status codes in the 2xx range indicate success, 3xx redirection (i.e. "try again, but over here"), 4xx something was wrong with the request, and 5xx something went wrong on the server's side.
 		For more information on HTTP, see https://developer.mozilla.org/en-US/docs/Web/HTTP (or read RFC 2616 to get it straight from the source: https://tools.ietf.org/html/rfc2616).
 		[b]Note:[/b] When performing HTTP requests from a project exported to HTML5, keep in mind the remote server may not allow requests from foreign origins due to [url=https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS]CORS[/url]. If you host the server in question, you should modify its backend to allow requests from foreign origins by adding the [code]Access-Control-Allow-Origin: *[/code] HTTP header.
+		[b]Note:[/b] SSL/TLS support is currently limited to TLS 1.0, TLS 1.1, and TLS 1.2. Attempting to connect to a TLS 1.3-only server will return an error.
 	</description>
 	<tutorials>
 		<link>https://docs.godotengine.org/en/3.2/tutorials/networking/http_client_class.html</link>

doc/classes/HTTPRequest.xml

@@ -65,6 +65,7 @@
 		    texture_rect.texture = texture
 		[/codeblock]
 		[b]Note:[/b] When performing HTTP requests from a project exported to HTML5, keep in mind the remote server may not allow requests from foreign origins due to [url=https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS]CORS[/url]. If you host the server in question, you should modify its backend to allow requests from foreign origins by adding the [code]Access-Control-Allow-Origin: *[/code] HTTP header.
+		[b]Note:[/b] SSL/TLS support is currently limited to TLS 1.0, TLS 1.1, and TLS 1.2. Attempting to connect to a TLS 1.3-only server will return an error.
 	</description>
 	<tutorials>
 		<link>https://docs.godotengine.org/en/3.2/tutorials/networking/http_request_class.html</link>