test: fix flaky repo verify (#10743)

The test was flaky because `ipfs repo verify` doesn't detect corruption
of the empty directory block (served from memory even when corrupted on
disk). Exclude both empty file and empty directory blocks from random
corruption to make the test reliable.

---------

Co-authored-by: Andrew Gillis <11790789+gammazero@users.noreply.github.com>

test/sharness/t0086-repo-verify.sh

@@ -24,7 +24,10 @@ sort_rand() {
 }
 
 check_random_corruption() {
-  to_break=$(find "$IPFS_PATH/blocks" -type f -name '*.data' | sort_rand | head -n 1)
+  # Exclude well-known blocks from corruption as they cause test flakiness:
+  # - CIQL7TG2PB52XIZLLHDYIUFMHUQLMMZWBNBZSLDXFCPZ5VDNQQ2WDZQ.data: empty file block
+  # - CIQFTFEEHEDF6KLBT32BFAGLXEZL4UWFNWM4LFTLMXQBCERZ6CMLX3Y.data: empty directory block (has special handling, served from memory even when corrupted on disk)
+  to_break=$(find "$IPFS_PATH/blocks" -type f -name '*.data' | grep -v -E "CIQL7TG2PB52XIZLLHDYIUFMHUQLMMZWBNBZSLDXFCPZ5VDNQQ2WDZQ.data|CIQFTFEEHEDF6KLBT32BFAGLXEZL4UWFNWM4LFTLMXQBCERZ6CMLX3Y.data" | sort_rand | head -n 1)
 
   test_expect_success "back up file and overwrite it" '
     cp "$to_break" backup_file &&