Apply the right tag for linux fuchsia cipd packages. (#46123)

The cipd packages were all being uploaded and tagged with git:HEAD.

Bug: flutter/flutter#126461

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: godofredoc

ci/builders/linux_fuchsia.json

@@ -163,7 +163,7 @@
                 "name": "Upload to CIPD for arch: arm64",
                 "parameters": [
                     "--engine-version",
-                    "HEAD",
+                    "${REVISION}",
                     "--target-arch",
                     "arm64",
                     "--out-dir",
@@ -180,7 +180,7 @@
                 "name": "Upload to CIPD for arch: x64",
                 "parameters": [
                     "--engine-version",
-                    "HEAD",
+                    "${REVISION}",
                     "--target-arch",
                     "x64",
                     "--out-dir",