CI: Trigger Windows build when a tag is pushed

AppVeyor ran our CI build when both branches and tags were pushed.  This
is necessary to support signing with SignPath.io, since we only sign
releases and not pre-releases.  However, due to an oversight in
9af8cca75c, the global on: dictionary
excluded tag pushes.

To simulate the previous AppVeyor CI environment:
- Run all jobs regardless of whether a branch or a tag was pushed.
- Use the if: key to exclude all jobs except "windows" from tag pushes.

.github/workflows/build.yml

@@ -2,13 +2,12 @@ name: Build
 
 on:
   push:
-    branches:
-      - '**'
   pull_request:
   workflow_dispatch:
 
 jobs:
   linux:
+    if: ${{!contains(github.ref, 'refs/tags/')}}
     runs-on: ubuntu-latest
     steps:
       - name: Set global environment variables
@@ -49,6 +48,7 @@ jobs:
         run: |
           aws s3 sync --acl public-read --delete $HOME/src/ljt.nightly/latest/files/ s3://libjpeg-turbo-pr/${{env.BRANCH}}/${{github.job}}/
   macos:
+    if: ${{!contains(github.ref, 'refs/tags/')}}
     runs-on: macos-13
     steps:
       - name: Set global environment variables
@@ -87,12 +87,19 @@ jobs:
   windows:
     runs-on: windows-2025
     steps:
+      - name: Check out code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
       - name: Set global environment variables
         shell: bash
         run: |
-          echo "BRANCH=${GITHUB_BASE_REF:-${GITHUB_REF#refs/heads/}}" >$GITHUB_ENV
-      - name: Check out code
-        uses: actions/checkout@v4
+          if [[ $GITHUB_REF == refs/tags/* ]]; then
+            RAWBRANCH=$(git branch -r --contains $GITHUB_REF)
+            echo "BRANCH=${RAWBRANCH##*/}" >$GITHUB_ENV
+          else
+            echo "BRANCH=${GITHUB_BASE_REF:-${GITHUB_REF#refs/heads/}}" >$GITHUB_ENV
+          fi
       - name: Set up build
         shell: bash
         run: |
@@ -181,6 +188,7 @@ jobs:
           github-artifact-id: ${{steps.upload-unsigned-artifact.outputs.artifact-id}}
           wait-for-completion: true
   linux-asan-ubsan:
+    if: ${{!contains(github.ref, 'refs/tags/')}}
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
@@ -205,6 +213,7 @@ jobs:
           JSIMD_FORCENONE=1 ctest -j$NUMCPUS
           popd
   linux-jpeg7:
+    if: ${{!contains(github.ref, 'refs/tags/')}}
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
@@ -230,6 +239,7 @@ jobs:
           JSIMD_FORCENONE=1 ctest -j$NUMCPUS
           popd
   linux-jpeg8:
+    if: ${{!contains(github.ref, 'refs/tags/')}}
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
@@ -255,6 +265,7 @@ jobs:
           JSIMD_FORCENONE=1 ctest -j$NUMCPUS
           popd
   linux-msan:
+    if: ${{!contains(github.ref, 'refs/tags/')}}
     runs-on: ubuntu-latest
     steps:
       - name: Check out code