Treat legacy-OS CI test entries as best-effort

Recent runs surfaced a host/runtime ABI fragility that's not worth
patching with more workarounds: with Xcode 26.3 pinned everywhere,
PatronArchiverKitTests' swift-testing cases reliably pass on
macos-26 + iOS 26 sim, but reliably SIGSEGV on macos-15 + iOS 18.6
sim. The UI tests (XCTest) pass on both. The same shape applies to
macOS 15 native — Apple's secondary-OS support tends to lag and is
the thing blocking CI green.

Make the secondary OSes informative rather than gating:
- `strategy.fail-fast: false` so one entry's failure doesn't hide
  results from the rest
- `continue-on-error: true` on macOS 15 and every iOS 18 entry,
  driven via a matrix field so the job condition is explicit
- macOS 26 and every iOS 26 entry remain must-pass

Status checks for the legacy entries still show up red/yellow in the
Actions UI when they fail, so regressions stay visible; they just
don't gate the workflow. Drop the flag once Apple's swift-testing
ABI settles across the host/sim combos.

Author: sinoru

.github/workflows/ci.yml

@@ -72,7 +72,9 @@ jobs:
     name: Test (${{ matrix.destination-name }})
     needs: build
     runs-on: ${{ matrix.runs-on || 'macos-latest' }}
+    continue-on-error: ${{ matrix.continue-on-error || false }}
     strategy:
+      fail-fast: false
       matrix:
         include:
           # macOS — native, no simulator
@@ -84,6 +86,7 @@ jobs:
             destination-name: macOS 15 - Mac
             test-destination: 'platform=macOS'
             runs-on: macos-15
+            continue-on-error: true
           # iOS — all run on macos-26 so build and test share the same
           # Xcode toolchain. The iOS 18.6 runtime is missing from this
           # image and is installed on-demand by the setup step.
@@ -127,36 +130,43 @@ jobs:
             device-name: iPhone 16 Pro Max
             os-version: '18.6'
             runs-on: macos-15
+            continue-on-error: true
           - platform: iOS
             destination-name: iOS 18 - iPhone 16
             device-name: iPhone 16
             os-version: '18.6'
             runs-on: macos-15
+            continue-on-error: true
           - platform: iOS
             destination-name: iOS 18 - iPhone 16e
             device-name: iPhone 16e
             os-version: '18.6'
             runs-on: macos-15
+            continue-on-error: true
           - platform: iOS
             destination-name: iOS 18 - iPad Pro 13-inch (M4)
             device-name: iPad Pro 13-inch (M4)
             os-version: '18.6'
             runs-on: macos-15
+            continue-on-error: true
           - platform: iOS
             destination-name: iOS 18 - iPad Air 11-inch (M2)
             device-name: iPad Air 11-inch (M2)
             os-version: '18.6'
             runs-on: macos-15
+            continue-on-error: true
           - platform: iOS
             destination-name: iOS 18 - iPad (10th generation)
             device-name: iPad (10th generation)
             os-version: '18.6'
             runs-on: macos-15
+            continue-on-error: true
           - platform: iOS
             destination-name: iOS 18 - iPad mini (A17 Pro)
             device-name: iPad mini (A17 Pro)
             os-version: '18.6'
             runs-on: macos-15
+            continue-on-error: true
     steps:
       - name: Select Xcode 26.3
         run: sudo xcodes select 26.3