[release-1.19] fix : make ambient work with intermidiary certs

[istio-testing]

Manual cherrypick required.

#680 failed to apply on top of branch "release-1.19":

Applying: fix istio/istio#46995 - work with intermidiary certs
Using index info to reconstruct a base tree...
M	src/tls/boring.rs
Falling back to patching base and 3-way merge...
Auto-merging src/tls/boring.rs
CONFLICT (content): Merge conflict in src/tls/boring.rs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 fix istio/istio#46995 - work with intermidiary certs
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

[dhawton]

#688

[hanxiaop]

Fixed by #688