ci: 5 retries for cargo (#6903)

cc https://github.com/paritytech/ci_cd/issues/1038

.cargo/config.toml

@@ -9,3 +9,7 @@ rustdocflags = [
 CC_x86_64_unknown_linux_musl = { value = ".cargo/musl-gcc", force = true, relative = true }
 CXX_x86_64_unknown_linux_musl = { value = ".cargo/musl-g++", force = true, relative = true }
 CARGO_WORKSPACE_ROOT_DIR = { value = "", relative = true }
+
+[net]
+retry = 5
+# git-fetch-with-cli = true # commented because there is a risk that a runner can be banned by github