[8.2.0] Fix metadata mnemonic field (#25780)

This was unintentionally changed to using the progress message in
f6aaa32.

Closes #25724.

PiperOrigin-RevId: 741609220
Change-Id: Ie68cd6c72dffa4be55c80df91429eafb9b9b8fc1

Commit
d2ff273

Co-authored-by: Fabian Meumertzheim <[email protected]>

Author: bazel-io

src/main/java/com/google/devtools/build/lib/remote/util/TracingMetadataUtils.java

@@ -55,7 +55,7 @@ public static RequestMetadata buildMetadata(
         buildRequestId,
         commandId,
         actionId,
-        actionMetadata != null ? actionMetadata.getProgressMessage() : null,
+        actionMetadata != null ? actionMetadata.getMnemonic() : null,
         actionMetadata != null && actionMetadata.getOwner().getLabel() != null
             ? actionMetadata.getOwner().getLabel().getCanonicalForm()
             : null,