Raise CI tests timeout to 15min (#3247)

Author: DouweM

.github/workflows/ci.yml

@@ -138,7 +138,7 @@ jobs:
   test:
     name: test on ${{ matrix.python-version }} (${{ matrix.install.name }})
     runs-on: ubuntu-latest
-    timeout-minutes: 10
+    timeout-minutes: 15
     strategy:
       fail-fast: false
       matrix:
@@ -183,7 +183,7 @@ jobs:
   test-lowest-versions:
     name: test on ${{ matrix.python-version }} (lowest-versions)
     runs-on: ubuntu-latest
-    timeout-minutes: 10
+    timeout-minutes: 15
     strategy:
       fail-fast: false
       matrix: