chore: revert "ci: exclude internal/librariangen/** on unrelated checks" (#3960)

Reverts #3953. Due to the change, GitHub
Actions stopped running the checks while the checks are still marked as
required. Tried this in
#3959 (comment).

<img width="1742" height="1336" alt="image"
src="https://github.com/user-attachments/assets/513fb435-65a9-4841-b3ca-d79a00fe1687"
/>

The documentation about this GitHub Actions behavior is
https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/collaborating-on-repositories-with-code-quality-features/troubleshooting-required-status-checks#handling-skipped-but-required-checks
:

> If a workflow is skipped due to [path
filtering](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#onpushpull_requestpull_request_targetpathspaths-ignore),
[branch
filtering](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#onpull_requestpull_request_targetbranchesbranches-ignore)
or a [commit
message](https://docs.github.com/en/actions/managing-workflow-runs/skipping-workflow-runs),
then checks associated with that workflow will remain in a "Pending"
state. A pull request that requires those checks to be successful will
be blocked from merging.
> 
> If, however, a job within a workflow is skipped due to a conditional,
it will report its status as "Success". For more information, see [Using
conditions to control job
execution](https://docs.github.com/en/actions/using-jobs/using-conditions-to-control-job-execution).

I didn't find usages of a file path filter in the condition of a job
within a workflow.


https://github.com/googleapis/sdk-platform-java/blob/main/.github/workflows/verify_library_generation.yaml#L8
is is a good example how to skip the main job
library-generation-unit-tests, by introducing the
should-run-library-generation-tests job.

Author: suztomo

.github/workflows/ci.yaml

@@ -3,8 +3,6 @@ on:
     branches:
       - main
   pull_request:
-    paths-ignore:
-      - 'internal/librariangen/**'
 name: ci
 jobs:
   build:

.github/workflows/dependency_compatibility_test.yaml

@@ -4,8 +4,6 @@ on:
   pull_request:
     branches:
       - 'main'
-    paths-ignore:
-      - 'internal/librariangen/**'      
   workflow_dispatch:
     inputs:
       dependencies-list:

.github/workflows/hermetic_library_generation.yaml

@@ -16,8 +16,6 @@
 name: Hermetic library generation upon generation config change through pull requests
 on:
   pull_request:
-    paths-ignore:
-      - 'internal/librariangen/**'
 
 env:
   REPO_FULL_NAME: ${{ github.event.pull_request.head.repo.full_name }}

.github/workflows/java_compatibility_check.yaml

@@ -15,8 +15,6 @@
 # downstream client libraries before they are released.
 on:
   pull_request:
-    paths-ignore:
-      - 'internal/librariangen/**'  
 name: Java 8 compatibility check
 jobs:
   java8-compatibility-check:

.github/workflows/sonar.yaml

@@ -5,8 +5,6 @@ on:
       - main
   pull_request:
     types: [opened, synchronize, reopened]
-    paths-ignore:
-      - 'internal/librariangen/**'
 jobs:
   build:
     name: Build

.github/workflows/verify_library_generation.yaml

@@ -1,7 +1,5 @@
 on:
   pull_request:
-    paths-ignore:
-      - 'internal/librariangen/**'
 
 name: verify_library_generation
 jobs: