Prevent trailing commas inside expression funcs (`hashFiles`) from triggering workflow crash

[eugengi]

Describe the bug

🛈 I must admit that this may not be a bug and is subject to the project author's decision.

I've had my workflows crash several times due to having a trailing comma used in the hashFiles input. These can be added manually or through linters/formatters. In my case, it's a learned habit, for a few reasons (cleaner vcs diffs, editing, ...). This minor formatting detail raises a TemplateValidationErrors syntax error and crashes a running pipeline (workflow).

To Reproduce

Steps to reproduce the behavior:

1. Create a workflow step containing an expression function with a trailing comma:

- name: Cache dependencies
  uses: actions/cache@v4
  with:
    path: ~/.cache/uv
    key: python-cache-${{ hashFiles('pyproject.toml', 'uv.lock', ) }}

2. Trigger/run the workflow.
3. Observe the syntax/parser initialization failure in the logs [error:: TemplateValidationErrors]

Expected Behavior

The expression syntax parsing logic can ignore the trailing comma when it precedes a closing parenthesis. ). This aligns better with modern config parser standards (imo) and also prevents minor syntax elements from breaking pipelines.

Screenshots

Metadata

Package/Area

• Expressions
• Workflow Parser
• Language Service
• Language Server

Package Version
v1.x.y

Additional context
N/A