Fix m.location.yaml scheme (#1507)

* Fix m.location.yaml scheme

This appears to have been mixed up while refactoring
f1f32d3a15 (diff-eb879a272497c490480df3e07215d058ace2fa0bf456447786f299995fb467ef)

* Create 1507.clarification

changelogs/client_server/newsfragments/1507.clarification

@@ -0,0 +1 @@
+Clarify `m.location` scheme by partially reverting [f1f32d3](https://github.com/matrix-org/matrix-spec/commit/f1f32d3a15c325ee8aa9d2c6bafd96c38069bb53). Contributed by @HarHarLinks.

data/event-schemas/schema/m.room.message$m.location.yaml

@@ -20,8 +20,8 @@ properties:
         properties:
           thumbnail_url:
             description: |-
-              The URL to the thumbnail of the file. Only present if the
+              The URL to a thumbnail of the location being represented.
-              thumbnail is unencrypted.
+              Only present if the thumbnail is unencrypted.
             type: string
           thumbnail_file:
             description: |-