ci: add free-threading tests (#238)

Author: Lancetnik

.github/workflows/tests.yml

@@ -14,11 +14,13 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t"]
         pydantic-version: ["pydantic-v1", "pydantic-v2"]
         exclude:
           - python-version: "3.14"
             pydantic-version: "pydantic-v1"
+          - python-version: "3.14t"
+            pydantic-version: "pydantic-v1"
       fail-fast: false
 
     steps:
@@ -59,7 +61,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t"]
       fail-fast: false
 
     steps: