Fix yamllint warnings

Author: alecw

.github/workflow-templates/bican-mccarroll-R-package.yml

@@ -1,7 +1,8 @@
+---
 # Workflow derived from https://github.com/r-lib/actions/tree/v2/examples
 # Need help debugging build failures?
 # Start at https://github.com/r-lib/actions#where-to-find-help
-on:
+"on":
   push:
     branches:
       - "$default-branch"

.github/workflow-templates/bican-mccarroll-python-package.yml

@@ -1,6 +1,6 @@
+---
 name: "Python unit tests for a package"
-
-on:
+"on":
   push:
     branches:
       - "$default-branch"

.github/workflow-templates/bican-mccarroll-roxygen.yml

@@ -1,7 +1,8 @@
+---
 # Workflow derived from dplyr/.github/workflows/pr-commands.yaml
 # Need help debugging build failures?
 # Start at https://github.com/r-lib/actions#where-to-find-help
-on:
+"on":
   issue_comment:
     types:
       - "created"