Add support for .tools-versions (#531)

Closes: #504

.github/workflows/test.yml

@@ -187,6 +187,22 @@ jobs:
             exit 1
           fi
 
+  test-tool-versions-file-version:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - name: Install from .tools-versions file
+        id: setup-uv
+        uses: ./
+        with:
+          version-file: "__tests__/fixtures/.tool-versions"
+      - name: Correct version gets installed
+        run: |
+          if [ "$(uv --version)" != "uv 0.5.15" ]; then
+            echo "Wrong uv version: $(uv --version)"
+            exit 1
+          fi
+
   test-checksum:
     runs-on: ${{ matrix.inputs.os }}
     strategy:
@@ -635,6 +651,7 @@ jobs:
       - test-uv-file-version
       - test-version-file-version
       - test-version-file-hash-version
+      - test-tool-versions-file-version
       - test-checksum
       - test-with-explicit-token
       - test-uvx