2021 tech alert date format

docs/tech-alerts-changelog/previous-years/2021.md

@@ -3,7 +3,7 @@
 :::{include} ./_components/previous-years-introduction.md
 :::
 
-## 2021-07-16: Collection 3 Landsat data now available
+## 16 Jul 2021: Collection 3 Landsat data now available
 
 Thanks to the [Geoscience Australia Landsat Collection Upgrade (video)](https://www.youtube.com/watch?v=BNEIG91lu44), 
 our data catalogue now includes Collection 3 data for DEA Surface Reflectance, also available through [OWS](https://ows.dea.ga.gov.au/). 
@@ -17,6 +17,6 @@ Users of Collection 2 are encouraged to use Collection 3 data.
 A staged decommissioning of Collection 2 is underway and will continue into 2022.
 Questions can be raised to [email protected]
 
-## 2021-04-15: New user guide - accessing data via AWS
+## 15 Apr 2021: New user guide - accessing data via AWS
 
 Added a new guide to accessing DEA data via [Amazon Web Services](/guides/setup/AWS/data_and_metadata/).