TST: Bump the python 3.10 test version from beta3 to rc1

Backport of numpy#19612.

Author: BvB93

.github/workflows/build_test.yml

@@ -56,7 +56,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.8, 3.9, 3.10.0-beta.3]
+        python-version: [3.8, 3.9, 3.10.0-rc.1]
     steps:
     - uses: actions/checkout@v2
       with: