Simplify stub binary update workflow.

.github/workflows/update-binary.yml

@@ -2,7 +2,7 @@ name: Update binary
 on:
   push:
     tags:
-    - '*-b*'
+    - 'b*'
 
 jobs:
   build-stubs:
@@ -16,14 +16,10 @@ jobs:
       env:
         TAG_NAME: ${{ github.ref }}
       run: |
-        export TAG=$(basename $TAG_NAME)
+        export BUILD_NUMBER=$(basename $TAG_NAME)
         export PYTHON_TAG=$(python -c "print('.'.join('${{ matrix.python-version }}'.split('.')[:2]))")
-        export BRIEFCASE_VERSION="${TAG%-*}"
-        export BUILD_NUMBER="${TAG#*-}"
 
-        echo "TAG=${TAG}" | tee -a $GITHUB_ENV
         echo "PYTHON_TAG=${PYTHON_TAG}" | tee -a $GITHUB_ENV
-        echo "BRIEFCASE_VERSION=${BRIEFCASE_VERSION}" | tee -a $GITHUB_ENV
         echo "BUILD_NUMBER=${BUILD_NUMBER}" | tee -a $GITHUB_ENV
 
     - name: Checkout Template
@@ -37,12 +33,7 @@ jobs:
     - name: Install Dependencies
       run: |
         python -m pip install --upgrade pip
-        if [ "${{ env.BRIEFCASE_VERSION }}" == "dev" ]; then
-          # We're on the development template; use development Briefcase
-          python -m pip install git+https://github.com/beeware/briefcase.git
-        else
-          python -m pip install briefcase==${{ env.BRIEFCASE_VERSION }}
-        fi
+        python -m pip install git+https://github.com/beeware/briefcase.git
 
     - name: Generate Xcode App Template
       run: |