Update country names to match official names (sz: Kingdom of Eswatini, tr: Republic of Türkiye)

Closes https://github.com/hampusborgos/country-flags/pull/142

countries.json

@@ -216,7 +216,7 @@
     "SV": "El Salvador",
     "SX": "Sint Maarten (Dutch part)",
     "SY": "Syrian Arab Republic",
-    "SZ": "Swaziland",
+    "SZ": "Kingdom of Eswatini",
     "TC": "Turks and Caicos Islands",
     "TD": "Chad",
     "TF": "French Southern Territories",
@@ -228,7 +228,7 @@
     "TM": "Turkmenistan",
     "TN": "Tunisia",
     "TO": "Tonga",
-    "TR": "Turkey",
+    "TR": "Republic of Türkiye",
     "TT": "Trinidad and Tobago",
     "TV": "Tuvalu",
     "TW": "Taiwan (Republic of China)",