add Python 3.9-rc to CI build

Author: belm0

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: ['3.6', '3.7', '3.8']
+        python: ['3.6', '3.7', '3.8', '3.9.0-rc.2']
         arch: ['x86', 'x64']
         lsp: ['']
         lsp_extract_file: ['']
@@ -59,7 +59,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: ['3.6', '3.7', '3.8']
+        python: ['3.6', '3.7', '3.8', '3.9.0-rc.2']
         check_formatting: ['0']
         extra_name: ['']
         include:
@@ -87,7 +87,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: ['3.6', '3.7', '3.8']
+        python: ['3.6', '3.7', '3.8', '3.9.0-rc.2']
     steps:
       - name: Checkout
         uses: actions/checkout@v2