doc: rename good first contrib label

Now `good first issue`.

PR-URL: #16150
Refs: #16149
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Joyee Cheung <[email protected]>
Reviewed-By: Yuta Hiroto <[email protected]>
Reviewed-By: Daniel Bevenius <[email protected]>
Reviewed-By: Daijiro Wachi <[email protected]>

Author: Fishrock123

doc/onboarding-extras.md

@@ -66,7 +66,7 @@ Please use these when possible / appropriate
 * `confirmed-bug` - Bugs you have verified exist
 * `discuss` - Things that need larger discussion
 * `feature request` - Any issue that requests a new feature (usually not PRs)
-* `good first contribution` - Issues suitable for newcomers to process
+* `good first issue` - Issues suitable for newcomers to process
 
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