Switch light GitHub workflows to ubuntu-slim runner

Switch lightweight CI workflows to the ubuntu-slim runner to save
resources. These workflows do not require significant compute and can
run on the 1-vCPU slim runner.

Workflows updated:
- pr-gh-workflow-approve.yaml
- pr-verifer.yml
- pr-link-check.yaml
- yamllint.yaml

Note: zizmor.yml is excluded because the zizmor-action fails on
ubuntu-slim (missing dependencies).

Signed-off-by: Dong Ma <winterma.dong@gmail.com>

Author: larainema

.github/workflows/pr-gh-workflow-approve.yaml

@@ -13,7 +13,7 @@ permissions: {}
 jobs:
   approve:
     name: Approve on ok-to-test
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
 
     permissions:
       actions: write

.github/workflows/pr-link-check.yaml

@@ -12,7 +12,7 @@ concurrency:
 
 jobs:
   check-links-pr:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
 
     steps:
     - name: Clone repository

.github/workflows/pr-verifer.yml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   check-title:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     steps:
     - name: Check out repository
       uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2

.github/workflows/yamllint.yaml

@@ -9,7 +9,7 @@ permissions:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     steps:
     - name: Install yamllint
       run: sudo apt-get update && sudo apt-get install -y yamllint