roles: bump macOS staging taskcluster_version toward 107.0.0

[rcurranmoz]

Automated monthly Taskcluster worker-version bump for the macOS staging pools.

Latest stable taskcluster: 107.0.0

Proposed staging bumps (capped per each pool's macOS/Go-toolchain ceiling):

• gecko_t_osx_1400_r8_staging: 100.5.0 → 107.0.0
• gecko_t_osx_1500_m4_staging: 100.5.0 → 107.0.0

Validate before merging

Push one try run per staging pool (these pools aren't in normal try routing). Each is a
minimal smoke that just exercises the worker binary (claim -> run -> upload); use the
suite that actually generates on each platform post-migration:

# 1500 / m4
./mach try fuzzy --all-tasks --worker-override t-osx-1500-m4=releng-hardware/gecko-t-osx-1500-m4-staging -q "'test-macosx1500-aarch64/opt 'xpcshell !vms"

# 1400 / Sonoma  (macosx1470-64 only generates cppunittest/gtest now; mochitests moved to m4)
./mach try fuzzy --all-tasks --worker-override t-osx-1400-r8=releng-hardware/gecko-t-osx-1400-r8-staging -q "'test-macosx1470-64/opt 'cppunittest"

# 1015 / Catalina
./mach try fuzzy --all-tasks --worker-override t-osx-1015-r8=releng-hardware/gecko-t-osx-1015-r8-staging -q "'test-macosx1015-64-qr/opt 'xpcshell"

(Or comment /try-mac 1500 | /try-mac 1400 | /try-mac 1015 on this PR to deploy the
branch to that staging pool automatically.) Staging hosts pick up the new binary on their
next reboot (cached). After staging is green, bump the prod roles in a separate PR.

Opened by .github/workflows/taskcluster-binary-bump.yml. Do not auto-merge.