niv motoko-base: update c7774995 -> 990dc3b4 (#4429)

## Changelog for motoko-base:
Branch: next-moc
Commits: [dfinity/motoko-base@c7774995...990dc3b4](dfinity/motoko-base@c777499...990dc3b)

* [`8073a606`](dfinity/motoko-base@8073a60) ci: publish Mops packages on tag creation ([dfinity/motoko-base⁠#620](https://togithub.com/dfinity/motoko-base/issues/620))
* [`8c100c44`](dfinity/motoko-base@8c100c4) Motoko 0.11.0
* [`fd095993`](dfinity/motoko-base@fd09599) chore: bump `mops` versions
* [`c19ec1ae`](dfinity/motoko-base@c19ec1a) bump to `actions/checkout@v4`
* [`482c0259`](dfinity/motoko-base@482c025) bump to `actions/setup-node@v4`

nix/sources.json

@@ -75,10 +75,10 @@
         "homepage": null,
         "owner": "dfinity",
         "repo": "motoko-base",
-        "rev": "c7774995a5e271339dff11e16474ece959cc4b60",
-        "sha256": "10zfybm940bdbx1a1z614127r8bnjrxyq3qm6d3zn27l32y248k4",
+        "rev": "990dc3b4cbd7d1e0d20031fb17b4e52271406ca7",
+        "sha256": "0mdfm2bawim3d4419pvzrmvyib9l72xh5mkir4qqhlyr1bacpvj4",
         "type": "tarball",
-        "url": "https://github.com/dfinity/motoko-base/archive/c7774995a5e271339dff11e16474ece959cc4b60.tar.gz",
+        "url": "https://github.com/dfinity/motoko-base/archive/990dc3b4cbd7d1e0d20031fb17b4e52271406ca7.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "motoko-matchers": {