CI: refactor shell-bash requirement

Signed-off-by: Andrei Horodniceanu <a.horodniceanu@proton.me>

Author: the-horo

.github/workflows/main.yml

@@ -9,6 +9,9 @@ concurrency:
 
 jobs:
   main:
+    defaults:
+      run:
+        shell: bash
     strategy:
       fail-fast: false
       matrix:
@@ -27,12 +30,9 @@ jobs:
         with:
           compiler: ${{ matrix.dc }}
       - name: Build
-        shell: bash
         run: make -j$N DMD=$DMD
       - name: Test
-        shell: bash
         run: make -j$N DMD=$DMD test
       - name: 'Windows: Build and test with MODEL=32'
         if: runner.os == 'Windows'
-        shell: bash
         run: make -j$N DMD=$DMD MODEL=32 all test