workspace: return to pre nix-shell directory before running bazel

Change-Id: I64ec0f26e2b7fd4ec9497bc59d68df438f3496d4
Reviewed-on: https://review.monogon.dev/c/monogon/+/2579
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/tools/bazel b/tools/bazel
index 4db2421..13fdda9 100755
--- a/tools/bazel
+++ b/tools/bazel
@@ -31,6 +31,7 @@
   cd "${DIR}/../"
 
   export COMMAND="bazel $*"
+  export PWD="$OLDPWD"
   exec nix-shell
 fi