Test coverage for ECHO for reply schema validation (valkey-io#1549)

After valkey-io#1545 disabled some tests for reply schema validation, we now have
another issue that ECHO is not covered.

```
WARNING! The following commands were not hit at all:
  echo
ERROR! at least one command was not hit by the tests
```

This patch adds a test case for ECHO in the unit/other test suite. I
haven't checked if there are more commands that aren't covered.

Signed-off-by: Viktor Söderqvist <[email protected]>

Author: zuiderkwast

.github/workflows/daily.yml

@@ -1150,7 +1150,7 @@ jobs:
     if: |
       (github.event_name == 'workflow_dispatch' ||
         (github.event_name == 'schedule' && github.repository == 'valkey-io/valkey') ||
-        (github.event_name == 'pull_request' && github.event.pull_request.base.ref != 'unstable')) &&
+        (github.event_name == 'pull_request' && (contains(github.event.pull_request.labels.*.name, 'run-extra-tests') || github.event.pull_request.base.ref != 'unstable'))) &&
       !contains(github.event.inputs.skipjobs, 'reply-schema')
     steps:
       - name: prep

tests/unit/other.tcl

@@ -30,6 +30,10 @@ start_server {tags {"other"}} {
         }
     }
 
+    test {Coverage: ECHO} {
+        assert_equal bang [r ECHO bang]
+    }
+
     test {SAVE - make sure there are all the types as values} {
         # Wait for a background saving in progress to terminate
         waitForBgsave r