Bump actions/setup-python from 5 to 6

Bumps [actions/setup-python](https://github.com/actions/setup-python) from 5 to 6.
- [Release notes](https://github.com/actions/setup-python/releases)
- [Commits](actions/setup-python@v5...v6)

---
updated-dependencies:
- dependency-name: actions/setup-python
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/build-nuget.yml

@@ -40,7 +40,7 @@ jobs:
     # ───────────────────────────── Repository & tools ────────────────────────────
     - uses: actions/checkout@v4
 
-    - uses: actions/setup-python@v5
+    - uses: actions/setup-python@v6
 
     - name: Install meson
       run: pip install meson

.github/workflows/ci.yml

@@ -202,7 +202,7 @@ jobs:
         buildType: [Debug, Release]
     runs-on: windows-latest
     steps:
-    - uses: actions/setup-python@v5
+    - uses: actions/setup-python@v6
     - name: Install meson
       run: pip install meson
     - name: Checkout
@@ -224,7 +224,7 @@ jobs:
   windows-msvc-openssl:
     runs-on: windows-latest
     steps:
-    - uses: actions/setup-python@v5
+    - uses: actions/setup-python@v6
     - name: Install meson
       run: pip install meson
     - name: Install OpenSSL