fix: Add shopt -s nullglob to dependencies script

This prevents processing the unexpanded glob "**/.flattened-pom.xml" in repos which do not flatten any POMs.

Source-Author: dpcollins-google <[email protected]>
Source-Date: Sat Jun 19 18:35:58 2021 -0400
Source-Repo: googleapis/synthtool
Source-Sha: 87254ac89a9559864c0a245d6b150406439ce3d8
Source-Link: googleapis/synthtool@87254ac

Author: yoshi-automation

.kokoro/dependencies.sh

@@ -14,6 +14,7 @@
 # limitations under the License.
 
 set -eo pipefail
+shopt -s nullglob
 
 ## Get the directory of the build script
 scriptDir=$(realpath $(dirname "${BASH_SOURCE[0]}"))

synth.metadata

@@ -11,7 +11,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "1c0c698705e668ccb3d68556ae7260f16ce63a6e"
+        "sha": "87254ac89a9559864c0a245d6b150406439ce3d8"
       }
     }
   ],