ci: format all YAML with `yq`

`yq` is the YAML query tool, used for manipulating YAML files. This
change uses the following command to read in and to pretty-print every
YAML file in this repository:

    for x in $(find . -name '*.yaml'); do
        yq -i -P -oy $x
    done

This makes it a bit easier to automate synchronisation between staging
and upstream, as yq always pretty-prints the entire document when
manipulating files.

Signed-off-by: Chris Kay <chris.kay@arm.com>
Change-Id: If973766fa26500d5320612422d1b4999b23439d3
diff --git a/TF-A-LTS2.12.yaml b/TF-A-LTS2.12.yaml
index 19db3ba..6f9278c 100644
--- a/TF-A-LTS2.12.yaml
+++ b/TF-A-LTS2.12.yaml
@@ -5,10 +5,10 @@
     filter-queue: true
     filter-executors: true
     columns:
-        - status
-        - weather
-        - job
-        - last-success
-        - last-failure
-        - last-duration
-        - build-button
+      - status
+      - weather
+      - job
+      - last-success
+      - last-failure
+      - last-duration
+      - build-button