Bug 1874432 [wpt PR 43971] - Add META.yml to mediacapture-insertable-streams folder and add some reviewers, a=testonly

Automatic update from web-platform-tests
Add META.yml to mediacapture-insertable-streams folder and add some reviewers (#43971)

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wpt-commits: e926548e859f4afd8f612254715051957cfdc68d
wpt-pr: 43971

testing/web-platform/tests/mediacapture-insertable-streams/META.yml

@@ -0,0 +1,6 @@
+spec: https://w3c.github.io/mediacapture-transform/
+suggested_reviewers:
+  - alvestrand
+  - guidou
+  - youennf
+  - jan-ivar