Modify applicable platform description

Author: ophub

.github/workflows/build-armbian-arm64-server-image.yml

@@ -403,5 +403,5 @@ jobs:
             - Default password: 1234
             - Install command: armbian-install
             - Update command: armbian-update
-            ### Armbian Image Verification
-            - sha256sum
+            ### Applicable platform
+            - arm64

.github/workflows/build-armbian-using-official-image.yml

@@ -385,5 +385,5 @@ jobs:
             - Default password: 1234
             - Install command: armbian-install
             - Update command: armbian-update
-            ### Armbian Image Verification
-            - sha256sum
+            ### Applicable platform
+            - arm64

.github/workflows/build-armbian-using-releases-files.yml

@@ -387,5 +387,5 @@ jobs:
             - Default password: 1234
             - Install command: armbian-install
             - Update command: armbian-update
-            ### Armbian Image Verification
-            - sha256sum
+            ### Applicable platform
+            - arm64