Re-enable the yamllint truthy rule

Previously we disabled the `truthy` rule due to Ansible's use of
`yes`/`no` for boolean values. That is no longer the case and the
default configuration used by ansible-lint now has this rule enabled.
The use of `on` as a key in GitHub Actions workflow syntax means we
needed to add disable-line comments for the truthy rule.

.github/workflows/build.yml

@@ -1,7 +1,7 @@
 ---
 name: build
 
-on:
+on:  # yamllint disable-line rule:truthy
   merge_group:
     types:
       - checks_requested

.github/workflows/sync-labels.yml

@@ -1,7 +1,7 @@
 ---
 name: sync-labels
 
-on:
+on:  # yamllint disable-line rule:truthy
   push:
     paths:
       - .github/labels.yml

.yamllint

@@ -49,7 +49,3 @@ rules:
     forbid-explicit-octal: true
     # Do not allow implicit octal values (those beginning with a leading 0).
     forbid-implicit-octal: true
-
-  # yamllint doesn't like when we use yes and no for true and false,
-  # but that's pretty standard in Ansible.
-  truthy: disable