[sw] Use default environment for srec_cat

This commit pulls in the default shell environment when invoking srec_cat
allowing for systems where srec_cat is not installed in the usual path.

Signed-off-by: Martin Lueker-Boden <martin.lueker-boden@wdc.com>

rules/opentitan.bzl

diff --git a/rules/opentitan.bzl b/rules/opentitan.bzl
index f4f8928..9e124f5 100644
--- a/rules/opentitan.bzl
+++ b/rules/opentitan.bzl
@@ -413,6 +413,7 @@
         # This this executable is expected to be installed (as required by the
         # srecord package in apt-requirements.txt).
         executable = "srec_cat",
+        use_default_shell_env = True,
     )
     return [DefaultInfo(
         files = depset(outputs),