macos-12 runner is deprecated

See actions/runner-images#10721

Newer runner does not include Tcl/Tk or SWIG, so we have to add these to the
setup.

.github/workflows/build.yml

@@ -1,7 +1,7 @@
 # Build, test and upload executables to GitHub
 # depends on pre-installed software; see image definitions:
 #  - https://github.com/actions/runner-images/blob/main/images/linux/Ubuntu2404-Readme.md
-#  - https://github.com/actions/runner-images/blob/main/images/macos/macos-12-Readme.md
+#  - https://github.com/actions/runner-images/blob/main/images/macos/macos-15-Readme.md
 # We use these tools from the runner images: git, gcc/XCode/MSVC, swig, Tcl/Tk on MacOS, pkg-config
 
 # TODO: not building svs_viewer ('Cannot find GL, GLU, not building svs_viewer' and 'Cannot find opengl32, glu32, not building svs_viewer')
@@ -31,7 +31,7 @@ jobs:
           # Use v24 beta for now to get newer SWIG; TODO: change back to ubuntu-latest once it points to v24
           ubuntu-24.04,
           # latest available X86_64 target
-          macos-12,
+          macos-15,
           # latest is ARM
           macos-latest,
         ]
@@ -56,12 +56,12 @@ jobs:
         if: startsWith(matrix.os, 'ubuntu-')
         run: sudo apt-get update && sudo apt-get install tcl-dev
 
-      - name: Setup tcl (macos-latest)
-        if: matrix.os == 'macos-latest'
+      - name: Setup tcl (macos)
+        if: startsWith(matrix.os, 'macos')
         run: brew install tcl-tk
 
-      - name: Setup SWIG (macos-latest)
-        if: matrix.os == 'macos-latest'
+      - name: Setup SWIG (macos)
+        if: startsWith(matrix.os, 'macos')
         run: brew install swig
 
       - name: build
@@ -285,7 +285,7 @@ jobs:
             # 20.04 to preserve compatibility with testing stage
             ubuntu-20.04,
             # latest available X86_64 target
-            macos-12,
+            macos-15,
             # latest is ARM
             macos-latest,
 
@@ -318,8 +318,8 @@ jobs:
       #   if: matrix.os == 'macos-latest'
       #   run: brew install tcl-tk
 
-      - name: Setup SWIG (macos-latest)
-        if: matrix.os == 'macos-latest'
+      - name: Setup SWIG (macos)
+        if: startsWith(matrix.os, 'macos')
         run: brew install swig
 
       - name: Setup SWIG (windows-latest)
@@ -371,7 +371,7 @@ jobs:
           # linux target which supports all python versions we want to install for
           - ubuntu-20.04
             # latest available X86_64 target
-          - macos-12
+          - macos-15
             # latest is ARM
           - macos-latest
           - windows-latest