ci(esdk): add version-ambiguity reason to duplicate-aws-lc 'why'

Author: Lucas McDonald

.github/workflows/rust_duplicate_deps.yml

@@ -1,7 +1,9 @@
 # Fails CI if a direct aws-lc-sys / aws-lc-fips-sys version differs from the one
 # aws-lc-rs pulls in transitively. Two versions compile two separate copies of
 # AWS-LC -- roughly 2x the native build time and a larger binary for customers
-# building our code. The fix is to match the direct -sys version to aws-lc-rs.
+# building our code -- and leave it unclear which version is actually in use, so
+# behavior can diverge if the two differ. The fix is to match the direct -sys
+# version to aws-lc-rs.
 name: Rust Duplicate aws-lc Dependency Check
 
 on:
@@ -71,7 +73,7 @@ jobs:
             want=$(cargo tree $args -p aws-lc-rs 2>/dev/null | grep -oE "${crate} v[0-9]+(\.[0-9]+)+" | head -1 | sed 's/.* v//' || true)
 
             echo "::error::Duplicate ${crate} in the ${label} build: Cargo.toml declares \"${have}\", aws-lc-rs pulls v${want}."
-            echo "Why it matters: two versions compile two separate copies of AWS-LC -- roughly 2x the native build time and a larger binary for customers building our code."
+            echo "Why it matters: two versions compile two separate copies of AWS-LC -- ~2x the native build time and a larger binary for customers building our code -- and it is unclear which version is actually in use, so our library's behavior can diverge if the two differ."
             echo "Fix: open a PR changing ${crate} in AwsEncryptionSDK/runtimes/rust/Cargo.toml from \"${have}\" to \"${want}\", then verify with: cargo tree -d${args:+ $args}"
           }