CI: Move git install to earlier in the build for Debian Docker container

We gotta have git on the CLI, or else the code isn't checked out via git,
it's downloaded as a tarball and extracted that way...

We need to be in the actual git repo for later steps of the build workflow!

.github/workflows/build.yml

@@ -31,6 +31,10 @@ jobs:
     container: ${{ matrix.image }}
 
     steps:
+    - name: Install git
+      if: ${{ runner.os == 'Linux' }}
+      run: apt-get update && apt-get install -y git
+
     - name: Checkout the latest code
       uses: actions/checkout@v3
 
@@ -44,10 +48,6 @@ jobs:
       with:
         python-version: ${{ env.PYTHON_VERSION }}
 
-    - name: Install git
-      if: ${{ runner.os == 'Linux' }}
-      run: apt-get update && apt-get install -y git
-
     - name: Setup Git Submodule
       run: |
         git submodule init