ci: change test internal libwasmvm binary triggered only build PR

[loloicci]

This PR changes the trigger of the test of internal libwasmvm binaries.
This is always triggered before this PR, and this PR changes it triggered only PR by the libwasmvm build bot.

Description

wasmvm has 2 tests for PR for the main branch, before this PR.

• Building libwasmvm binaries from the source and doing tests with it
• Doing tests with libwasmvm included in internal/api directory

An error is caused in CI when internal/api's libwasmvm is old, though we have a CI building libwasmvm binaries after the main branch is updated.
As a result, if PR publishers think that they leave building libwasmvm on CI after the merge, internal libwasmvm's test fails. (now we have this issue on #142)

To solve this, we change the trigger of the test of internal/api's libwasmvm binaries.

Types of changes

• Bug fix (changes which fixes an issue)
• New feature (changes which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• ETC (build, ci, docs, perf, refactor, style, test)

Checklist

• I followed the contributing guidelines.
• I have updated the documentation accordingly. (not needed)
• I have added tests to cover my changes. (not needed)
• The PR title and commits are followed conventional commit form.

[170210]

LGTM