ci: try Python 3.15 release candidate (DRAFT)

Point CI workflows at the 3.15 RC (allow-prereleases already enabled)
and add the 3.15 trove classifier, to document which dependencies and
tests are not yet ready. Must stay in DRAFT until Python 3.15 has a
production release (early October). Requested in #15081.

Author: priya-sundaram-dev

.github/workflows/build.yml

@@ -17,7 +17,7 @@ jobs:
           cache-dependency-glob: uv.lock
       - uses: actions/setup-python@v7
         with:
-          python-version-file: pyproject.toml
+          python-version: 3.15
           allow-prereleases: true
       - run: uv sync --group=test
       - name: Run tests

.github/workflows/directory_writer.yml

@@ -11,7 +11,7 @@ jobs:
           fetch-depth: 0
       - uses: actions/setup-python@v7
         with:
-          python-version-file: pyproject.toml
+          python-version: 3.15
           allow-prereleases: true
       - name: Write DIRECTORY.md
         run: |

.github/workflows/project_euler.yml

@@ -25,7 +25,7 @@ jobs:
       - uses: astral-sh/setup-uv@v7
       - uses: actions/setup-python@v7
         with:
-          python-version-file: pyproject.toml
+          python-version: 3.15
           allow-prereleases: true
       - run: uv sync --group=euler-validate --group=test
       - run: uv run pytest --doctest-modules --cov-report=term-missing:skip-covered --cov=project_euler/ project_euler/
@@ -43,7 +43,7 @@ jobs:
       - uses: astral-sh/setup-uv@v7
       - uses: actions/setup-python@v7
         with:
-          python-version-file: pyproject.toml
+          python-version: 3.15
           allow-prereleases: true
       - run: uv sync --group=euler-validate --group=test
       - run: uv run pytest scripts/validate_solutions.py

.github/workflows/sphinx.yml

@@ -36,7 +36,7 @@ jobs:
       - uses: astral-sh/setup-uv@v7
       - uses: actions/setup-python@v7
         with:
-          python-version-file: pyproject.toml
+          python-version: 3.15
           allow-prereleases: true
       - run: uv sync --group=docs
       - uses: actions/configure-pages@v6

pyproject.toml

@@ -7,6 +7,7 @@ requires-python = ">=3.14"
 classifiers = [
   "Programming Language :: Python :: 3 :: Only",
   "Programming Language :: Python :: 3.14",
+  "Programming Language :: Python :: 3.15",
 ]
 dependencies = [
   "beautifulsoup4>=4.12.3",