Use colored output on CI for Doctest

GitHub Actions output is not considered a TTY, so colored output
must be forced.

(cherry picked from commit dec26e15b3)

.github/workflows/linux_builds.yml

@@ -150,7 +150,7 @@ jobs:
         run: |
           ${{ matrix.bin }} --version
           ${{ matrix.bin }} --help
-          ${{ matrix.bin }} --test --headless
+          ${{ matrix.bin }} --headless --test --force-colors
 
       # Check class reference
       - name: Check for class reference updates

.github/workflows/macos_builds.yml

@@ -72,4 +72,4 @@ jobs:
         run: |
           ${{ matrix.bin }} --version
           ${{ matrix.bin }} --help
-          ${{ matrix.bin }} --test
+          ${{ matrix.bin }} --test --force-colors

.github/workflows/windows_builds.yml

@@ -75,4 +75,4 @@ jobs:
         run: |
           ${{ matrix.bin }} --version
           ${{ matrix.bin }} --help
-          ${{ matrix.bin }} --test
+          ${{ matrix.bin }} --test --force-colors