json-glib: Update textprox/json-glib to 1.6.2

Overview of changes for 1.6
==============================
• Add getters with default fallback for JsonObject [Emmanuele Bassi]
• #26 - Clarify some expections of the json_object_get_*_member APIs [Debarshi Ray]
• #29 - Improve reproducibility of the build [Ravish Bhatia]
• Use json_node_unref() with g_autoptr() [Robert Ancell]
• Clarify documentation regarding programmer errors [Philip Withnall]
• Fix getting immutable root nodes from empty input [Philip Withnall]
• Fix various memory leaks [Philip Withnall, Emmanuele Bassi]
• Add `--output` option to json-glib-format [Emmanuele Bassi]
• Refresh the build [Emmanuele Bassi]
• Add glib as a fallback sub-project [Xavier Claessens]
• Don't error with MSVC C4819 warning [Seungha Yang]
• Fix nullable annotation [Niels De Graef]
• Allow disabling tests when building [Stéphane Cerveau]
• #39 - Fix default deserialization method for JsonSerializable [Jeremy Philippe]
• Stop string to GVariant conversion failing due to unrelated errno changes [Robert Ancell]
• Support loading files via memory mapping [Philip Withnall]
• #33 - Add a symbol version to all exported symbols [Simon McVittie]
• #48 - Fix build with Clang 11 [Dimitry Andric]
• Stop using deprecated g_object_newv() constructor [Emmanuele Bassi]
• Add ordered iteration to JsonObjectIter [Emmanuele Bassi]
• #46 - Document nullability of `json_from_string()` [Emmanuele Bassi]
• #45 - Properly detect multiple top-level statements [Emmanuele Bassi]
• #41, #22 - Fix library versions on Darwin [Tom Schoonjans]
• Fix build reproducibility [!33, Alexander Kanavin]
• #26 - Fix parsing of UTF-16 surrogate pairs [James Westman]
• #56 - Ignore UTF-8 BOM [Jan-Michael Brummer]

(cirnatdan)