CI: python-version should be a string, not a float

Author: DimitriPapadopoulos

.github/workflows/contrib.yml

@@ -32,7 +32,7 @@ jobs:
     strategy:
       matrix:
         os: ['ubuntu-latest']
-        python-version: [3.8]
+        python-version: ['3.8']
         nipype-extras: ['dev']
         check: ['specs', 'style']
     env:

.github/workflows/tests.yml

@@ -91,15 +91,15 @@ jobs:
     strategy:
       matrix:
         os: ['ubuntu-20.04']
-        python-version: [3.7, 3.8, 3.9, "3.10"]
+        python-version: ['3.7', '3.8', '3.9', '3.10']
         check: ['test']
         pip-flags: ['']
         depends: ['REQUIREMENTS']
         deb-depends: [false]
         nipype-extras: ['doc,tests,profiler']
         include:
           - os: ubuntu-20.04
-            python-version: 3.8
+            python-version: '3.8'
             check: test
             pip-flags: ''
             depends: REQUIREMENTS