Fix YAML syntax error in vcpkg install step

PowerShell here-strings require content at column 0 which breaks YAML
block scalars. Use backtick newlines in a regular string instead.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: cataphract

.github/workflows/tests.yml

@@ -94,12 +94,8 @@ jobs:
         run: |
           $tripletDir = "$env:RUNNER_TEMP\vcpkg-triplets"
           New-Item -ItemType Directory -Force -Path $tripletDir | Out-Null
-          Set-Content "$tripletDir\x64-windows-static-md.cmake" @'
-set(VCPKG_TARGET_ARCHITECTURE x64)
-set(VCPKG_CRT_LINKAGE dynamic)
-set(VCPKG_LIBRARY_LINKAGE static)
-set(VCPKG_BUILD_TYPE release)
-'@
+          Set-Content "$tripletDir\x64-windows-static-md.cmake" `
+            "set(VCPKG_TARGET_ARCHITECTURE x64)`nset(VCPKG_CRT_LINKAGE dynamic)`nset(VCPKG_LIBRARY_LINKAGE static)`nset(VCPKG_BUILD_TYPE release)"
           C:\vcpkg\vcpkg.exe install libarchive `
             --triplet x64-windows-static-md `
             --overlay-triplets="$tripletDir" `