Add GitHub Actions and Pub to the ecosystems list (#74)

* Add GitHub Actions and Pub to the ecosystems list

This adds GitHub Actions and Pub to the documented list of defined ecosystems. The description for Pub is the wording taken directly from their website, but open to feedback if you'd like it to follow a specific pattern.

There are no validations on the ecosystems defined in the schema docs, so the validation JSON has not been updated.

* Clarify formatting of Actions name

docs/schema.md

@@ -382,6 +382,8 @@ The defined ecosystems are:
 | `Debian` | The Debian package ecosystem; the `name` is the name of the source package. The ecosystem string might optionally have a `:<RELEASE>` suffix to scope the package to a particular Debian release. `<RELEASE>` is a numeric version specified in the [Debian distro-info-data](https://debian.pages.debian.net/distro-info-data/debian.csv). For example, the ecosystem string "Debian:7" refers to the Debian 7 (wheezy) release.  |
 | `Hex` | The package manager for the Erlang ecosystem; the `name` is a Hex package name.  |
 | `Android`  | The Android ecosystem; the `name` field is the Android component name that the patch applies to, as shown in the [Android Security Bulletins](https://source.android.com/security/bulletin) such as `Framework`, `Media Framework` and `Kernel Component`. The exhaustive list of components can be found at the [Appendix](#android-ecosystem-components). |
+| `GitHub Actions` | The GitHub Actions ecosystem; the `name` field is the action's repository name with owner e.g. `{owner}/{repo}`. |
+| `Pub` | The package manager for the Dart ecosystem; the `name` field is a Dart package name. |
 | Your ecosystem here. | [Send us a PR](https://github.com/ossf/osv-schema/compare). |
 
 It is permitted for a database name (the DB prefix in the `id` field) and an