CI: use the preinstalled mingw-w64 and ninja on windows-latest

The setup-mingw step took 61s to `choco upgrade mingw`, downloading and
extracting a 102 MB 7z -- and the toolchain it installed was never used.
The chocolatey package relocates itself to C:\ProgramData\mingw64\mingw64\bin
while the action appends C:\ProgramData\chocolatey\lib\mingw\tools\install\mingw64\bin
to GITHUB_PATH, a path that does not exist, so the compiler lookup fell
through to the mingw-w64 that windows-latest already ships at C:\mingw64\bin
(gcc 15.2.0, ucrt, posix threads). The build logs confirm it:

    -- Check for working C compiler: C:/mingw64/bin/cc.exe - skipped
    -- The C compiler identification is GNU 15.2.0

The action's only real contribution was hardlinking cc.exe/c++.exe next to
the mingw binaries, which naming gcc/g++ in the cmake invocation makes
unnecessary.

gha-setup-ninja is dropped for the same reason: it downloaded ninja 1.12.1
while the image already has 1.13.2 on PATH.

Also bumps actions/checkout v1 -> v4.

Job time goes from ~2m46s to ~1m40s.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: bsergean

.github/workflows/unittest_windows_gcc.yml

@@ -11,20 +11,16 @@ jobs:
   windows:
     runs-on: windows-latest
     steps:
-    - uses: actions/checkout@v1
-    - uses: seanmiddleditch/gha-setup-ninja@master
-    - uses: bsergean/setup-mingw@d79ce405bac9edef3a1726ef00554a56f0bafe66
+    - uses: actions/checkout@v4
+    # No toolchain setup step: windows-latest ships mingw-w64 (gcc, ucrt, posix
+    # threads) at C:\mingw64\bin and ninja, both already on PATH.
     - run: |
         mkdir build
         cd build
-        cmake -GNinja -DCMAKE_CXX_COMPILER=c++ -DCMAKE_C_COMPILER=cc -DUSE_WS=1 -DUSE_TEST=1 -DUSE_ZLIB=0 -DCMAKE_UNITY_BUILD=ON ..
+        cmake -GNinja -DCMAKE_CXX_COMPILER=g++ -DCMAKE_C_COMPILER=gcc -DUSE_WS=1 -DUSE_TEST=1 -DUSE_ZLIB=0 -DCMAKE_UNITY_BUILD=ON ..
     - run: |
         cd build
         ninja
     - run: |
         cd build
         ctest -V
-        # ninja test
-
-#- run: ../build/test/ixwebsocket_unittest.exe
-# working-directory: test