fix the github token env

Author: grl-wang

buildspec/linuxTests.yml

@@ -13,7 +13,7 @@ env:
         # followed by Error: Could not delete obsolete instance handle Error: ENOENT: no such file or directory, unlink <path>
         AWS_TOOLKIT_TEST_CACHE_DIR: '/tmp/.vscode-test/'
         AWS_TOOLKIT_TEST_USER_DIR: '/tmp/.vscode-test/user-data/'
-        GITHUB_TOKEN: ${GITHUB_READONLY_TOKEN}
+        GITHUB_TOKEN: $GITHUB_READONLY_TOKEN
 
 phases:
     install:

buildspec/packageTestVsix.yml

@@ -8,7 +8,7 @@ env:
         AWS_TOOLKIT_TEST_USER_DIR: '/tmp/'
         # needed or else webpack will cause it to run out of memory
         NODE_OPTIONS: '--max-old-space-size=8192'
-        GITHUB_TOKEN: ${GITHUB_READONLY_TOKEN}
+        GITHUB_TOKEN: $GITHUB_READONLY_TOKEN
 
 phases:
     install: