run-test: Fix diff output

The linux `diff` command can return non-zero exit code.  Ignore it.

Bug: 253419335
Test: modify expected output of a test and observe the failure
Change-Id: Ic7be706e79df21a9a0d4c4beeb437a300b55a722
diff --git a/test/run-test b/test/run-test
index 47208b0..cf859f0 100755
--- a/test/run-test
+++ b/test/run-test
@@ -966,14 +966,12 @@
     error("#################### stdout diffs")
     if run_checker == "yes":
       # Checker failures dump the whole CFG, so we output the whole diff.
-      run(f'diff --strip-trailing-cr -u "{expected_stdout}" "{test_stdout}"')
+      run(f'diff --strip-trailing-cr -u "{expected_stdout}" "{test_stdout}"', check=False)
     else:
-      run(f'diff --strip-trailing-cr -u "{expected_stdout}" "{test_stdout}" | tail -n 10000'
-         )
+      run(f'diff --strip-trailing-cr -u "{expected_stdout}" "{test_stdout}" | tail -n 10000', check=False)
     error("####################")
     error("#################### stderr diffs")
-    run(f'diff --strip-trailing-cr -u "{expected_stderr}" "{test_stderr}" | tail -n 10000'
-       )
+    run(f'diff --strip-trailing-cr -u "{expected_stderr}" "{test_stderr}" | tail -n 10000', check=False)
     error("####################")
     if strace == "yes":
       error("#################### strace output")