[CI] Use "ubuntu-slim" runner for lightweight workflows

Signed-off-by: Denis Krivenko <dnskrv88@gmail.com>

Author: dnskr

.github/workflows/docs.yml

@@ -32,7 +32,7 @@ concurrency:
 jobs:
   sphinx:
     name: sphinx-build
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     steps:
       - uses: actions/checkout@v6.0.2
       - uses: actions/setup-python@v6

.github/workflows/greetings.yml

@@ -27,7 +27,7 @@ on:
 
 jobs:
   greeting:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     permissions:
       issues: write
       pull-requests: write

.github/workflows/labeler.yml

@@ -26,7 +26,7 @@ permissions:
 
 jobs:
   triage:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     steps:
     - uses: actions/labeler@v5
       with:

.github/workflows/stale.yml

@@ -23,7 +23,7 @@ on:
 
 jobs:
   stale:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     permissions:
       pull-requests: write
     steps: