Adding Changedlog_Pending to ignore list of main GHA workflow (#347)

### Summary
- See #340 for
example - main workflow is triggered and fails on just codefreeze PRs.
It doesn't really need to run at all, it only triggered because
CHANGELOG_PENDING was not on the ignore list like CHANGELOG is

.github/workflows/main.yml

@@ -392,6 +392,7 @@ name: main
     - main
     paths-ignore:
     - CHANGELOG.md
+    - CHANGELOG_PENDING.md
     tags-ignore:
     - v*
     - sdk/*

CHANGELOG_PENDING.md

@@ -5,4 +5,5 @@
 - Fixed import by refactoring Read method of AgentPool resource + minor refactor [#311](https://github.com/pulumi/pulumi-pulumiservice/issues/311)
 - Fixing noisy diff in DS OIDC object [#330](https://github.com/pulumi/pulumi-pulumiservice/issues/330)
 
-### Miscellaneous
+### Miscellaneous
+- Added CHANGELOG_PENDING file to ignore-list of the `main` workflow [[#340](https://github.com/pulumi/pulumi-pulumiservice/issues/340)]