ci.yml: avoid full git clone (--depth=1)

Author: oech3

.github/workflows/ci.yml

@@ -102,7 +102,7 @@ jobs:
       id: build_grcov
       shell: bash
       run: |
-        git clone https://github.com/mozilla/grcov.git ~/grcov/
+        git clone --depth=1 https://github.com/mozilla/grcov.git ~/grcov/
         cd ~/grcov
         cargo install --path .
         cd -