doc: Prefer https:// over git://.

* doc/guix.texi (Continuous Integration): Use https:// in fictitious URLs.

doc/guix.texi

@@ -21377,12 +21377,12 @@ the @code{"custom-packages"} input, which is the equivalent of
                      (#:branch . "master")
                      (#:no-compile? . #t))
                     ((#:name . "config")
-                     (#:url . "git://git.example.org/config.git")
+                     (#:url . "https://git.example.org/config.git")
                      (#:load-path . ".")
                      (#:branch . "master")
                      (#:no-compile? . #t))
                     ((#:name . "custom-packages")
-                     (#:url . "git://git.example.org/custom-packages.git")
+                     (#:url . "https://git.example.org/custom-packages.git")
                      (#:load-path . ".")
                      (#:branch . "master")
                      (#:no-compile? . #t)))))))