run_test: acknowledge bashisms

If a test script uses bash extensions, it should not call /bin/sh
which is the POSIX shell (and no further assumptions should be made).
In the long run, we should rewrite that test for the POSIX shell, but
to quickly get rid of CI breakages, it is faster to acknowledge the
bash dependency.

--
Change-Id: I179a0d17ef663d473524d80de7dc660778c23acd
Reviewed-on: https://bazel-review.googlesource.com/#/c/6071
MOS_MIGRATED_REVID=133137841
diff --git a/src/test/shell/integration/run_test.sh b/src/test/shell/integration/run_test.sh
index d6c2028..ad986930 100755
--- a/src/test/shell/integration/run_test.sh
+++ b/src/test/shell/integration/run_test.sh
@@ -289,7 +289,7 @@
 EOF
 
   cat > some/testing/test.sh <<'EOF'
-#!/bin/sh
+#!/bin/bash
 set -ex
 echo "Got $@"
 i=1