bindgen: remove extra trailing space in check for --rust-edition flags (#3799)

The arguments would be passed as either `--rust-edition=2024` or
`--rust-edition`, `2024`, but either way the resulting entry from the
list comprehension on the right hand of the `not in` operator will
contain `"--rust-edition"` without the trailing space. This allows users
of the bindgen rules to specify their own explicit edition.

Tested:
  Works in our private repo, and didn't without this patch.

Co-authored-by: Krasimir Georgiev <krasimir@google.com>

Author: durin42

extensions/bindgen/private/bindgen.bzl

@@ -241,7 +241,7 @@ def _rust_bindgen_impl(ctx):
     args.add_all(ctx.attr.bindgen_flags)
 
     rust_toolchain = ctx.toolchains[Label("@rules_rust//rust:toolchain_type")]
-    if "--rust-edition " not in [f.split("=")[0] for f in ctx.attr.bindgen_flags]:
+    if "--rust-edition" not in [f.split("=")[0] for f in ctx.attr.bindgen_flags]:
         args.add("--rust-edition=%s" % rust_toolchain.default_edition)
 
     args.add(header)