docs(changelog): add #1435 fragment

changelog.d/1435-military-positionless-rows.md

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+- Military aircraft that leave the adsb.lol feed fade and are removed again.
+  The feed's routine position-less rows no longer mark every snapshot partial,
+  which kept vanished aircraft at full opacity for up to five minutes; those
+  rows keep only their own aircraft, and a likely-landed one still leaves on
+  the landed limit (Aditya, @Rohilalala, #1435).