Update 3.13 python versions to 3.13-dev

Author: schloerke

.github/py-shiny/setup/action.yaml

@@ -4,7 +4,7 @@ inputs:
   python-version:
     description: 'Python version to use'
     required: false
-    default: "3.12"
+    default: "3.13-dev"
 runs:
   using: "composite"
   steps:

.github/workflows/build-docs.yaml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.12"]
+        python-version: ["3.13-dev"]
       fail-fast: false
 
     steps:

.github/workflows/pytest.yaml

@@ -17,7 +17,7 @@ jobs:
     strategy:
       matrix:
         # "3.10" must be a string; otherwise it is interpreted as 3.1.
-        python-version: ["3.13", "3.12", "3.11", "3.10", "3.9"]
+        python-version: ["3.13-dev", "3.12", "3.11", "3.10", "3.9"]
         os: [ubuntu-latest, windows-latest, macOS-latest]
         exclude:
           - python-version: ${{ github.event.pull_request.draft && '3.11' }}
@@ -108,7 +108,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.13", "3.12", "3.11", "3.10", "3.9"]
+        python-version: ["3.13-dev", "3.12", "3.11", "3.10", "3.9"]
         browser: ["chromium", "firefox", "webkit"]
         exclude:
           - python-version: ${{ github.event.pull_request.draft && '3.11' }}
@@ -156,7 +156,7 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        python-version: ["3.13", "3.12", "3.11", "3.10", "3.9"]
+        python-version: ["3.13-dev", "3.12", "3.11", "3.10", "3.9"]
         browser: ["chromium", "firefox", "webkit"]
         exclude:
           - python-version: ${{ github.event.pull_request.draft && '3.11' }}