ci: Bump up versions and fix linting

.travis.yml

@@ -1,9 +1,9 @@
 language: python
 
 python:
-  - "3.7"
+  - "3.13"
 
-dist: focal
+dist: noble
 
 before_install:
   - sudo apt-get install -y libfftw3-dev

cmake/JoinPaths.cmake

@@ -6,7 +6,7 @@
 # https://github.com/jtojnar/cmake-snips
 #
 # Modelled after Python’s os.path.join
-# https://docs.python.org/3.7/library/os.path.html#os.path.join
+# https://docs.python.org/3.13/library/os.path.html#os.path.join
 # Windows not supported
 function(join_paths joined_path first_path_segment)
     set(temp_path "${first_path_segment}")