Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/add_source_to_release.yml

@@ -17,7 +17,7 @@ jobs:
 
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
           submodules: recursive

.github/workflows/build_container.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Login to GitHub Container Registry
         run: echo "${{ secrets.GITHUB_TOKEN }}" | docker login ghcr.io -u iqtree --password-stdin

.github/workflows/build_docs.yml

@@ -22,7 +22,7 @@ jobs:
     name: Fetch or Build IQ-TREE Static Library
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
           submodules: recursive
@@ -40,7 +40,7 @@ jobs:
     needs: build-iqtree
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
           submodules: recursive

.github/workflows/build_wheels.yml

@@ -30,7 +30,7 @@ jobs:
           platform_id: win_amd64
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
           submodules: recursive

.github/workflows/ci.yml

@@ -24,7 +24,7 @@ jobs:
         os: [ubuntu-latest, macos-15-intel, macos-15, windows-latest] # Intel linux, Intel Mac, ARM Mac, Windows
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
           submodules: recursive
@@ -46,7 +46,7 @@ jobs:
         os: [ubuntu-latest, macos-15-intel, macos-15, windows-latest] # Intel linux, Intel Mac, ARM Mac, Windows
         python-version: ["3.11", "3.12", "3.13"]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
           submodules: recursive
@@ -102,7 +102,7 @@ jobs:
         os: [ubuntu-latest]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
 
@@ -127,7 +127,7 @@ jobs:
         os: [ubuntu-latest]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
 
@@ -152,7 +152,7 @@ jobs:
         os: [ubuntu-latest]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
           submodules: recursive

.github/workflows/release.yml

@@ -30,7 +30,7 @@ jobs:
           platform_id: win_amd64
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
           submodules: recursive
@@ -87,7 +87,7 @@ jobs:
     name: Fetch or Build IQ-TREE Static Library
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
           submodules: recursive
@@ -105,7 +105,7 @@ jobs:
     needs: build-iqtree
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
           submodules: recursive