Add open_jdk to Linux linux_android_emulator.debug_x64 (flutter#173989)

Towards flutter#173986.

This build _never_ declared (either directly or through
`platform_properties`) that it required the Java JDK, and appears to
have been "accidentally" getting it installed via a (now expired) cache
of the Java JDK.

I'll file a separate issue of "should platform properties be inherited
by engine v2 sub-builds".

/cc @jason-simmons @gaaclarke for FYI.

Author: matanlurey

engine/src/flutter/ci/builders/linux_android_emulator.json

@@ -23,6 +23,10 @@
                 {
                     "dependency": "goldctl",
                     "version": "git_revision:720a542f6fe4f92922c3b8f0fdcc4d2ac6bb83cd"
+                },
+                {
+                    "dependency": "open_jdk",
+                    "version": "version:21"
                 }
             ],
             "name": "ci/android_emulator_debug_x64",