Add action typings with validation (#721)

I'd like to add machine-readable type hints for this action. They also
serve as a formal documentation on the types of action's inputs and
outputs, which is a standardized way of documenting these also for human
users. See https://github.com/typesafegithub/github-actions-typing for
details. Dozens of actions already provide typings this way.

In particular, this change will let the users of
https://github.com/typesafegithub/github-workflows-kt use this action in
a convenient, type-safe way from their Kotlin workflows. From the
binding service's metrics I see that this action is among the most
popular ones that doesn't have typings configured, so on behalf of the
users of this tool, I'm asking you to consider adding the typings.

.github/workflows/test.yml

@@ -1033,6 +1033,15 @@ jobs:
         env:
           GH_TOKEN: ${{ github.token }}
 
+  validate-typings:
+    runs-on: "ubuntu-latest"
+    steps:
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+        with:
+          persist-credentials: false
+      - name: Validate typings
+        uses: typesafegithub/github-actions-typing@184d97003b1300f6a10e286eb98c191e416ff02b # v2.2.1
+
   all-tests-passed:
     runs-on: ubuntu-latest
     needs:
@@ -1081,6 +1090,7 @@ jobs:
       - test-restore-python-installs
       - test-python-install-dir
       - test-act
+      - validate-typings
     if: always()
     steps:
       - name: All tests passed

action-types.yml

@@ -0,0 +1,71 @@
+# See https://github.com/typesafegithub/github-actions-typing
+
+inputs:
+  version:
+    type: string
+  version-file:
+    type: string
+  python-version:
+    type: string
+  activate-environment:
+    type: boolean
+  working-directory:
+    type: string
+  checksum:
+    type: string
+  github-token:
+    type: string
+  enable-cache:
+    type: enum
+    allowed-values:
+      - "true"
+      - "false"
+      - auto
+  cache-dependency-glob:
+    type: list
+    separator: "\n"
+    list-item:
+      type: string
+  restore-cache:
+    type: boolean
+  save-cache:
+    type: boolean
+  cache-suffix:
+    type: string
+  cache-local-path:
+    type: string
+  prune-cache:
+    type: boolean
+  cache-python:
+    type: boolean
+  ignore-nothing-to-cache:
+    type: boolean
+  ignore-empty-workdir:
+    type: boolean
+  tool-dir:
+    type: string
+  tool-bin-dir:
+    type: string
+  manifest-file:
+    type: string
+  add-problem-matchers:
+    type: boolean
+  resolution-strategy:
+    type: enum
+    allowed-values:
+      - highest
+      - lowest
+
+outputs:
+  uv-version:
+    type: string
+  uv-path:
+    type: string
+  uvx-path:
+    type: string
+  cache-hit:
+    type: boolean
+  cache-key:
+    type: string
+  venv:
+    type: string