Explicitly guard optional matrix steps in CI workflow (#89)

* Initial plan

* Guard optional matrix steps with explicit non-empty conditions

Co-authored-by: JohannesLorenz <1042576+JohannesLorenz@users.noreply.github.com>

* Use truthy check for optional matrix fields instead of != '' comparison

Co-authored-by: JohannesLorenz <1042576+JohannesLorenz@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: JohannesLorenz <1042576+JohannesLorenz@users.noreply.github.com>

Author: Copilot

.github/workflows/ccpp.yml

@@ -83,13 +83,13 @@ jobs:
         with:
           fetch-depth: 0
       - name: update system
-        if: ${{ matrix.config.enabled == 1 }}
+        if: ${{ matrix.config.enabled == 1 && matrix.config.update }}
         run: ${{ matrix.config.update }}
       - name: install deps (1)
-        if: ${{ matrix.config.enabled == 1 }}
+        if: ${{ matrix.config.enabled == 1 && matrix.config.deps1 }}
         run: ${{ matrix.config.deps1 }}
       - name: install deps (2)
-        if: ${{ matrix.config.enabled == 1 }}
+        if: ${{ matrix.config.enabled == 1 && matrix.config.deps2 }}
         run: ${{ matrix.config.deps2 }}
       - name: create build directory
         if: ${{ matrix.config.enabled == 1 }}