blackbox: Use "git add -A" to really stage all changes.

Otherwise we miss deleted files.

Explanation for the change from the Git docs:
- git add -A stages all changes
- git add . stages new files and modifications, without deletions
- git add -u stages modifications and deletions, without new files

PiperOrigin-RevId: 254744271
diff --git a/src/test/java/com/google/devtools/build/lib/blackbox/tests/workspace/GitRepositoryHelper.java b/src/test/java/com/google/devtools/build/lib/blackbox/tests/workspace/GitRepositoryHelper.java
index 0bced90..0db27f3 100644
--- a/src/test/java/com/google/devtools/build/lib/blackbox/tests/workspace/GitRepositoryHelper.java
+++ b/src/test/java/com/google/devtools/build/lib/blackbox/tests/workspace/GitRepositoryHelper.java
@@ -58,7 +58,7 @@
    *     code.
    */
   void addAll() throws Exception {
-    runGit("add", ".");
+    runGit("add", "-A");
   }
 
   /**