CI: Fix git.mk & post a quick flash link on PR builds (#670)

* CI: Fix git.mk & post a quick flash link on PR builds
* Makefile: optimize shell invocation in git helper, conditional dependency load.
* Github: better variable naming

Co-authored-by: Aleksandr Kutuzov <alleteam@gmail.com>

.github/workflows/lint_c.yml

@@ -43,19 +43,19 @@ jobs:
       - name: 'Build docker image'
         uses: ./.github/actions/docker
 
-      - name: 'Check syntax'
+      - name: 'Check code formatting'
         id: syntax_check
         uses: ./.github/actions/docker
         with:
           run: SET_GH_OUTPUT=1 /syntax_check.sh
 
-      - name: Report syntax errors
+      - name: Report code formatting errors
         if: failure() && steps.syntax_check.outputs.errors && github.event.pull_request
         uses: peter-evans/create-or-update-comment@v1
         with:
           issue-number: ${{ github.event.pull_request.number }}
           body: |
-            Please fix following syntax errors:
+            Please fix following code formatting errors:
             ```
             ${{ steps.syntax_check.outputs.errors }}
             ```