doc: Fix amount typo in release notes

See bitcoin#16524 (comment)

Author: MarcoFalke

doc/release-notes.md

@@ -92,7 +92,9 @@ Low-level changes
 Tests
 -----
 
-- `-fallbackfee` was 0 (disabled) by default for the main chain, but 20000 by default for the test chains. Now it is 0 by default for all chains. Testnet and regtest users will have to add fallbackfee=20000 to their configuration if they weren't setting it and they want it to keep working like before. (#16524)
+- `-fallbackfee` was 0 (disabled) by default for the main chain, but 0.0002 by default for the test chains. Now it is 0
+  by default for all chains. Testnet and regtest users will have to add `fallbackfee=0.0002` to their configuration if
+  they weren't setting it and they want it to keep working like before. (#16524)
 
 Credits
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