Update to Python 3.15 release candidate in CI and add trove classifier

.github/workflows/python-package.yml

diff --git a/.github/workflows/python-package.yml b/.github/workflows/python-package.yml
index 0662b31..2a3ec83 100644
--- a/.github/workflows/python-package.yml
+++ b/.github/workflows/python-package.yml
@@ -70,7 +70,7 @@
           - '3.12'
           - '3.13'
           - '3.14'
-          - '3.15-dev'
+          - '3.15'
           - 'pypy-3.11'
         include:
           # Free-threaded builds, run with the GIL disabled; the suite checks
@@ -78,7 +78,7 @@
           # so it is only set here.)
           - python-version: '3.14t'
             gil: '0'
-          - python-version: '3.15t-dev'
+          - python-version: '3.15t'
             gil: '0'
     runs-on: ubuntu-latest
     steps:

pyproject.toml

diff --git a/pyproject.toml b/pyproject.toml
index fadb918..fbe641c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -25,6 +25,7 @@
   "Programming Language :: Python :: 3.12",
   "Programming Language :: Python :: 3.13",
   "Programming Language :: Python :: 3.14",
+  "Programming Language :: Python :: 3.15",
   "Programming Language :: Python :: Implementation :: CPython",
   "Programming Language :: Python :: Implementation :: PyPy",
   "Topic :: Internet :: Name Service (DNS)",