Update Express types files, allow further upgrades (#5352)

Our versions for `@types/express` and `@types/express-serve-static-core`
have gotten a bit out of date. They are already upgraded on
`release-3.0` but that's not quite `latest` yet. Somehow despite the
fact that neither `express` nor `serve-static` have had a new version in
two years, the DefinitelyTyped packages for them keep getting
backwards-incompatible changes. This is apparently helpful for some
users who have upgraded some other packages.

Because of how finicky these types are (eg specific `@types/express`
versions depends on specific `@types/express-serve-static-core` versions
without appropriate version dependencies between them) I do generally
think it's best to depend on exact versions here. However I also don't
want to have to make any more AS2 releases. So I'm making these into
caret dependencies but don't intend to make a similar change on
`release-3.0`.

Fixes #5350.

package.json

@@ -67,7 +67,7 @@
     "@types/bunyan": "1.8.6",
     "@types/connect": "3.4.34",
     "@types/cors": "2.8.10",
-    "@types/express": "4.17.11",
+    "@types/express": "4.17.12",
     "@types/fast-json-stable-stringify": "2.0.0",
     "@types/hapi": "17.8.10",
     "@types/ioredis": "4.26.2",

packages/apollo-server-express/package.json

@@ -31,8 +31,8 @@
     "@types/accepts": "^1.3.5",
     "@types/body-parser": "1.19.0",
     "@types/cors": "2.8.10",
-    "@types/express": "4.17.11",
-    "@types/express-serve-static-core": "4.17.19",
+    "@types/express": "^4.17.12",
+    "@types/express-serve-static-core": "^4.17.21",
     "accepts": "^1.3.5",
     "apollo-server-core": "file:../apollo-server-core",
     "apollo-server-types": "file:../apollo-server-types",