Fix Windows build with msys2 secp256k1

.github/workflows/python-ci.yml

@@ -17,17 +17,28 @@ jobs:
       - uses: actions/setup-python@v4
         with:
           python-version: '3.11'
-      - name: Install build tools
+      - name: Install build tools (Linux/macOS)
+        if: runner.os != 'Windows'
         shell: bash
         run: |
           if [ "$RUNNER_OS" = "Linux" ]; then
             sudo apt-get update
             sudo apt-get install -y pkg-config build-essential
-          elif [ "$RUNNER_OS" = "macOS" ]; then
-            brew install pkg-config
           else
-            choco install pkgconfiglite -y
+            brew install pkg-config
           fi
+      - name: Install MSYS2 and libsecp256k1
+        if: runner.os == 'Windows'
+        id: msys
+        uses: msys2/setup-msys2@v2
+        with:
+          install: >-
+            mingw-w64-x86_64-toolchain
+            mingw-w64-x86_64-libsecp256k1
+      - name: Set libsecp256k1 path
+        if: runner.os == 'Windows'
+        shell: bash
+        run: echo "SECP256K1_LIB_DIR=${{ steps.msys.outputs.msys2-location }}/mingw64" >> $GITHUB_ENV
       - name: Cache pip
         uses: actions/cache@v3
         with: