Build: Stop testing on iOS 10

As of January 2025, iOS 10 is a tier 4 device on BrowserStack:
https://www.browserstack.com/device-tiers
That leads to devices with this iOS version often not being available and
failing our tests. Remove it from the test matrix. Also, add comments explaining
the status of tests on various iOS versions, including iOS 7 that we stopped
testing on a long time ago.

.github/workflows/browserstack.yml

@@ -48,9 +48,19 @@ jobs:
           - '__iOS_13'
           - '__iOS_12'
           - '__iOS_11'
-          - '__iOS_10'
+
+          # iOS 10 is a tier 4 device as of January 2025 and its availability
+          # is poor, leading to frequent test timeouts. Skip testing on it.
+          # See https://www.browserstack.com/device-tiers
+          # - '__iOS_10'
+
+          # Versions below are not officially supported by BrowserStack as
+          # they use emulators instead of real devices. We include them as
+          # long as they still work.
           - '__iOS_9'
           - '__iOS_8'
+          # iOS 7 emulators no longer work properly
+          # - '__iOS_7'
     steps:
       - name: Checkout
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2