git_repository: properly quote shallow argument

Since fully qualified timestamps for "--shallow_since" can have a
format like "1551301058 -0500" this argument needs to be quoted.
Do so. This could go unnoticed, as the git_repository rule always
falls back to full cloning; nevertheless, having shallow clones
not working can be a huge performance impact.

Change-Id: I853c128cc6413d6cb314277dbfd04c98c17f07b5
PiperOrigin-RevId: 236850530

tools/build_defs/repo/git.bzl

diff --git a/tools/build_defs/repo/git.bzl b/tools/build_defs/repo/git.bzl
index d766911..1c45dec 100644
--- a/tools/build_defs/repo/git.bzl
+++ b/tools/build_defs/repo/git.bzl
@@ -55,10 +55,10 @@
 ( cd {working_dir} &&
     if ! ( cd '{dir_link}' && [[ "$(git rev-parse --git-dir)" == '.git' ]] ) >/dev/null 2>&1; then
       rm -rf '{directory}' '{dir_link}'
-      git clone {shallow} '{remote}' '{directory}' || git clone '{remote}' '{directory}'
+      git clone '{shallow}' '{remote}' '{directory}' || git clone '{remote}' '{directory}'
     fi
     git -C '{directory}' reset --hard {ref} || \
-    ((git -C '{directory}' fetch {shallow} origin {ref}:{ref} || \
+    ((git -C '{directory}' fetch '{shallow}' origin {ref}:{ref} || \
       git -C '{directory}' fetch origin {ref}:{ref}) && git -C '{directory}' reset --hard {ref})
       git -C '{directory}' clean -xdf )
   """.format(