tools: be intentional about masking possible error in start-ci.sh

Revise start-ci.sh to conform with shellcheck 0.8.0 default checks.

Refs: https://www.shellcheck.net/wiki/SC2312

PR-URL: #41284
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

tools/actions/start-ci.sh

@@ -17,7 +17,7 @@ for pr in "$@"; do
     # Do we need to reset?
     gh pr edit "$pr" --add-label "$REQUEST_CI_FAILED_LABEL"
 
-    jq -n --arg content "<details><summary>Couldn't start CI</summary><pre>$(cat output)</pre></details>" > output.json
+    jq -n --arg content "<details><summary>Couldn't start CI</summary><pre>$(cat output || true)</pre></details>" > output.json
 
     gh pr comment "$pr" --body-file output.json