GHA: drop redundant shellcheck expression filter

GHA expressions are no longer used and no longer allowed in GHA scripts.

Follow-up to d7cf63bb05 #1609

Closes #2602

.github/workflows/ci.yml

@@ -81,7 +81,7 @@ jobs:
               echo '#!/usr/bin/env bash'
               echo 'set -eu'
               yq eval '.. | select(has("run") and (.run | type == "!!str")) | .run + "\ntrue\n"' "${f}"
-            } | sed -E 's|\$\{\{ .+ \}\}|GHA_EXPRESSION|g' | shellcheck -
+            } | shellcheck -
           done
 
       - name: 'shellcheck'