This does not change the version of rules_apple, it only pins the http
archive instead of fetching via git tag.
To avoid Bazel warnings of the following form since Bazel 3.3.1
```
DEBUG: Rule 'build_bazel_rules_apple' indicated that a canonical reproducible form can be obtained by modifying arguments commit = "ff6a37b24fcbbd525a5bf61692a12c810d0ee3c1", shallow_since = "1559833568 -0700" and dropping ["tag"]
DEBUG: Repository build_bazel_rules_apple instantiated at:
no stack (--record_rule_instantiation_callstack not enabled)
Repository rule git_repository defined at:
/home/aj/.cache/bazel/_bazel_aj/f66bee630c6a2cd906f92a0f5cdf8769/external/bazel_tools/tools/build_defs/repo/git.bzl:195:33: in <toplevel>
```
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Co-authored-by: Andreas Herrmann <andreas.herrmann@tweag.io>
