[deps] rev markdown, source_span, string_scanner

Revisions updated by `dart tools/rev_sdk_deps.dart`.

markdown (https://github.com/dart-lang/markdown/compare/93d0eee..9b61871):
  9b61871  2022-10-25  Kevin Moore  Make helper class private that should not have been exposed (#476)
  299964e  2022-10-26  le.chang  Return list for link nodes creation (#452)
  aee6a40  2022-10-25  Kevin Moore  validate code coverage on CI (#474)
  88f3f8a  2022-10-25  Zhiguang Chen  Fix html entity and numeric character references (#467)

source_span (https://github.com/dart-lang/source_span/compare/ff03af1..d1d47e5):
  d1d47e5  2022-10-25  Kevin Moore  Require Dart 2.18, update lints, latest pkg:lints, add dependabot (#88)

string_scanner (https://github.com/dart-lang/string_scanner/compare/2d84b16..10435a4):
  10435a4  2022-10-25  Kevin Moore  Update minimum SDK, latest pkg:lints, update CI actions (#48)

Change-Id: I94dbb0830600cb5304aaae16b2ae715bfc71411e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/265641
Auto-Submit: Devon Carew <[email protected]>
Commit-Queue: Nate Bosch <[email protected]>
Reviewed-by: Nate Bosch <[email protected]>

DEPS

@@ -139,7 +139,7 @@ vars = {
   "linter_rev": "f2c55484e8ebda0aec8c2fea637b3bd5b17258ca", # 1.28.0
   "lints_rev": "16bdefe1df529262a6596f79e91003ddbdbd3890",
   "logging_rev": "f322480fb9d9e83e677c08db6d09067059f7ff74",
-  "markdown_rev": "93d0eee771f6355be6737c2a865f613f6b105bf1",
+  "markdown_rev": "9b61871ab57da13211ab988c19ab79ea4a8cab0a",
   "markupsafe_rev": "8f45f5cfa0009d2a70589bcda0349b8cb2b72783",
   "matcher_rev": "6a9b83bbd73e50df2058b3e8e4aa301df49569c6",
   "mime_rev": "bf041aa372a27aae6f94e185aa0af3932b9de98b",
@@ -156,11 +156,11 @@ vars = {
   "shelf_rev": "39d820d4e32fc99c65f562786097487d597dcee1",
   "source_map_stack_trace_rev": "8d8078fcc81c8f7936805cd277198493e0b7fc62",
   "source_maps_rev": "b031e2cdbef5675ab9a92025202d323a5e7cc526",
-  "source_span_rev": "ff03af16474ce91c89eb3bc28182866f4cb6dfb0",
+  "source_span_rev": "d1d47e550b6f77ed9b4907339a8a5e430b9ca314",
   "sse_rev": "283568dd4865cc51e25370ed107fcbdb68759c22",
   "stack_trace_rev": "dce00134f6558086e8963e37d0b1ba0830862c01",
   "stream_channel_rev": "a5129ca44322a7024074ca38fb98e343dcb638c7",
-  "string_scanner_rev": "2d84b16d8ae03c3a8c2417b71abe0fe6de7d8bf6",
+  "string_scanner_rev": "10435a4f468e480273f78a6cfa1615c82446ef47",
   "sync_http_rev": "f5c1f18f579752112870fa2f1860470d28c6f605",
   "term_glyph_rev": "ec7cf7bb51ebb7d55760a1359f6697690dbc06ba",
   "test_descriptor_rev": "66f14ce9159f425da000ad105e0b890fe396c2b7",