misc: Add 'scheduler.yaml' workflow (#1307)

This is made to run on the 'stable' branch to schedule workflow runs on
the `develop` branch. This solves the problem of GitHub Workflows being
scheduled to only run on 'stable' branch' thus ignoring changes made to
them on 'develop'

With this schedule we no longer need to force a checkout of 'develop' in
the workflows. As such these have been removed.

The scheduled workflows are now triggered via "workflow_dispatch" via
the "scheduler.yaml" workflow

.github/workflows/compiler-tests.yaml

@@ -4,10 +4,7 @@
 name: Compiler Tests
 
 on:
-  # Runs every Friday from 7AM UTC
-    schedule:
-        - cron: 00 7 * * 5
-  # Allows us to manually start workflow for testing
+    # This is triggered weekly via the 'scheduler.yaml' workflow.
     workflow_dispatch:
 
 jobs:
@@ -25,10 +22,6 @@ jobs:
         container: ghcr.io/gem5/${{ matrix.image }}:latest
         steps:
             - uses: actions/checkout@v4
-              with:
-        # Scheduled workflows run on the default branch by default. We
-        # therefore need to explicitly checkout the develop branch.
-                  ref: develop
             - name: Compile build/ALL/gem5${{ matrix.opts }} with ${{ matrix.image }}
               run: /usr/bin/env python3 /usr/bin/scons --ignore-style build/ALL/gem5${{ matrix.opts }} -j$(nproc)
               timeout-minutes: 600 # 10 hours
@@ -47,10 +40,6 @@ jobs:
         container: ghcr.io/gem5/${{ matrix.image }}:latest
         steps:
             - uses: actions/checkout@v4
-              with:
-        # Scheduled workflows run on the default branch by default. We
-        # therefore need to explicitly checkout the develop branch.
-                  ref: develop
             - name: Compile build/${{ matrix.gem5-compilation }}/gem5${{ matrix.opts }} with ${{ matrix.image }}
               run: /usr/bin/env python3 /usr/bin/scons --ignore-style build/${{ matrix.gem5-compilation }}/gem5${{ matrix.opts }} -j$(nproc)
               timeout-minutes: 600 # 10 hours