Update gfortran in CI (#56)

* update the gfortran compiler to v12 as v10

* Use gfortran-13 for testing on Linux to see if it fixes things

* add additional CI test on gfortran 10

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Co-authored-by: Michael Schlottke-Lakemper <michael@sloede.com>

Author: andrewwinters5000

.github/workflows/ci.yml

@@ -24,10 +24,14 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-latest
+          - os: ubuntu-22.04
             compiler: gfortran-10
             cmake_generator: Unix Makefiles
             shell: bash
+          - os: ubuntu-latest
+            compiler: gfortran-13
+            cmake_generator: Unix Makefiles
+            shell: bash
           - os: macos-latest
             compiler: gfortran-12
             cmake_generator: Unix Makefiles