Added retry-option to work around occasional failure while checking out git...

Added retry-option to work around occasional failure while checking out git repo due to race condition.

.gitlab-ci.yml

@@ -8,6 +8,7 @@ rust-latest:
     - rustup show active-toolchain || rustup toolchain install
     - cargo build
     - cargo test
+  retry: 2
 
 rust-nightly:
   stage: build
@@ -16,3 +17,4 @@ rust-nightly:
     - cargo +nightly build
     - cargo +nightly test
   allow_failure: true
+  retry: 2