Remove redundant trigger types from workflow

[rdhar]

Description

Going by documentation, "By default, a workflow only runs when a pull_request event's activity type is opened, synchronize, or reopened".

As a result, there's no need to redefine those types explicitly again and the line can be safely removed for the exact same behaviour. This suggestion can be applied directly for commit.

Motivation and Context

This change only serves to prevent over-definition since the default/standard behaviour is the expected one in this case. All about getting more for less!

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My change depends on a change in the main opentofu repository.