actions: GH Attestation for GAM executables and packages

https://github.blog/changelog/2024-05-02-artifact-attestations-public-beta/

attest that GAM was built on GitHub actions to help end users validate they're running a legit GAM binary.

.github/workflows/build.yml

@@ -9,6 +9,7 @@ on:
 permissions:
   contents: read
   id-token: write
+  attestations: write
 
 defaults:
   run:
@@ -546,6 +547,9 @@ jobs:
           export gam="${gampath}/gam"
           echo "gampath=${gampath}" >> $GITHUB_ENV
           echo "gam=${gam}" >> $GITHUB_ENV
+          if [[ "${RUNNER_OS}" == "Windows" ]]; then
+               gam=$(cygpath -w "$gam")
+             fi
           echo -e "GAM: ${gam}\nGAMPATH: ${gampath}"
           # TEMP force everything back to one file.
           export PYINSTALLER_BUILD_ONEFILE="yes"
@@ -596,6 +600,12 @@ jobs:
           echo "GAM Version ${GAMVERSION}"
           echo "GAMVERSION=${GAMVERSION}" >> $GITHUB_ENV
 
+      - name: Attest Binary Provenance
+        uses: actions/attest-build-provenance@v1
+        if: matrix.goal == 'build'
+        with:
+          subject-path: ${{ env.gam }}
+
       - name: Linux/MacOS package
         if: runner.os != 'Windows' && matrix.goal == 'build'
         run: |
@@ -852,6 +862,15 @@ jobs:
           fi
           tar cJvvf cache.tar.xz $tar_folders
 
+      - name: Attest Build Archive Provenance
+        uses: actions/attest-build-provenance@v1
+        if: (github.event_name == 'push' || github.event_name == 'schedule') && matrix.goal == 'build'
+        with:
+          subject-path: |
+            gam*.tar.xz
+            gam*.zip
+            gam*.msi
+
       - name: Archive production artifacts
         uses: actions/upload-artifact@v4
         if: (github.event_name == 'push' || github.event_name == 'schedule') && matrix.goal != 'test'