feat(github_actions): Move xcb-errors commit ID to envvar

Signed-off-by: Lucas Schwiderski <lucas@lschwiderski.de>

.github/workflows/main.yml

@@ -71,6 +71,7 @@ jobs:
       SOURCE_DATE_EPOCH: ${{ matrix.source_date_epoch }}
       TEST_TIMEOUT: '100'
       CI: 'true'
+      XCB_ERRORS_SHA: '5d660ebe872cadcdc85de9d6f9afe05de629c030'
 
     steps:
       # Create a cache invalidation key based on the current year + week.
@@ -174,14 +175,14 @@ jobs:
           path: /tmp/xcb-errors
           # xcb-errors doesn't have versioned releases, so we checkout and cache by commit.
           # Make sure to keep this in sync with the `git checkout` below.
-          key: ${{ github.workflow }}-${{ runner.os }}-xcb-errors-5d660ebe872cadcdc85de9d6f9afe05de629c030
+          key: ${{ github.workflow }}-${{ runner.os }}-xcb-errors-${{ env.XCB_ERRORS_SHA }}
 
       - name: Install fresh xcb-errors
         if: steps.cache-xcb-errors.outputs.cache-hit != 'true'
         run: |
           git clone --recursive https://gitlab.freedesktop.org/xorg/lib/libxcb-errors.git /tmp/xcb-errors
           cd /tmp/xcb-errors
-          git checkout 5d660ebe872cadcdc85de9d6f9afe05de629c030
+          git checkout ${{ env.XCB_ERRORS_SHA }}
           ./autogen.sh --prefix=/usr
           make
           sudo make install