ci: skip lint presubmit on non-code changes (#2506)

## Description

Optimizes CI usage by skipping `lint` workflows for changes unrelated to
source code, such as documentation updates (`docs/**`, `**.md`) or other
GitHub configurations (`.github/**`).

To satisfy GitHub's **Required Status Checks**, "fallback" workflows
have been added. These workflows trigger *only* when the main workflows
are skipped and instantly report success, ensuring PRs don't get stuck
in a pending state.

**Note:** Direct edits to the workflow files themselves are explicitly
included in triggers to allow for self-testing.


## PR Checklist

> Thank you for opening a Pull Request! Before submitting your PR, there
are a
> few things you can do to make sure it goes smoothly:

- [ ] Make sure you reviewed

[CONTRIBUTING.md](https://github.com/googleapis/genai-toolbox/blob/main/CONTRIBUTING.md)
- [ ] Make sure to open an issue as a

[bug/issue](https://github.com/googleapis/genai-toolbox/issues/new/choose)
  before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)
- [ ] Make sure to add `!` if this involve a breaking change

🛠️ Fixes #<issue_number_goes_here>

Author: twishabansal

.github/workflows/lint.yaml

@@ -15,8 +15,20 @@
 name: lint
 on:
   pull_request:
+    paths:
+      - "**"
+      - "!docs/**"
+      - "!**.md"
+      - "!.github/**"
+      - ".github/workflows/lint.yaml"
   pull_request_target:
     types: [labeled]
+    paths:
+      - "**"
+      - "!docs/**"
+      - "!**.md"
+      - "!.github/**"
+      - ".github/workflows/lint.yaml"
 
 # Declare default permissions as read only.
 permissions: read-all

.github/workflows/lint_fallback.yaml

@@ -0,0 +1,41 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: lint
+
+on:
+  pull_request:
+    paths:
+      - "docs/**"
+      - "**.md"
+      - ".github/**"
+      - "!.github/workflows/lint.yaml"
+  pull_request_target:
+    paths:
+      - "docs/**"
+      - "**.md"
+      - ".github/**"
+      - "!.github/workflows/lint.yaml"
+
+permissions: read-all
+
+jobs:
+  lint:
+    name: lint
+    runs-on: ubuntu-latest
+    steps:
+      - name: Skip Lint
+        run: |
+          echo "Skipping lint for documentation/config-only changes."
+          echo "This job exists to satisfy the required status check."