Update to the latest package:source_span

Change-Id: I6f910af40bbcfadd74c1eb18b0f7f79d658f2986
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/225500
Reviewed-by: Jake Macdonald <jakemac@google.com>
Auto-Submit: Nate Bosch <nbosch@google.com>

.dart_tool/package_config.json

@@ -11,7 +11,7 @@
     "constraint, update this by running tools/generate_package_config.dart."
   ],
   "configVersion": 2,
-  "generated": "2021-12-10T17:31:54.553345",
+  "generated": "2021-12-22T16:24:00.538300",
   "generator": "tools/generate_package_config.dart",
   "packages": [
     {
@@ -629,7 +629,7 @@
       "name": "source_span",
       "rootUri": "../third_party/pkg/source_span",
       "packageUri": "lib/",
-      "languageVersion": "2.12"
+      "languageVersion": "2.14"
     },
     {
       "name": "sourcemap_testing",
@@ -817,4 +817,4 @@
       "languageVersion": "2.12"
     }
   ]
-}
+}