Fix type error in rust-analyzer rule

[UebelAndre]

Before this change, users would fail with the following error:

~/Code/rules_rust/examples (main ✔) bazel run @rules_rust//tools/rust_analyzer:gen_rust_project
INFO: Analyzed target @@rules_rust//tools/rust_analyzer:gen_rust_project (51 packages loaded, 2095 targets configured).
INFO: Found 1 target...
Target @@rules_rust//tools/rust_analyzer:gen_rust_project up-to-date:
  bazel-bin/external/rules_rust/tools/rust_analyzer/gen_rust_project
INFO: Elapsed time: 0.530s, Critical Path: 0.01s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
INFO: Running command line: bazel-bin/external/rules_rust/tools/rust_analyzer/gen_rust_project
Error: bazel build failed:(exit status: 1)
Computing main repo mapping:
Loading:
Loading: 0 packages loaded
Analyzing: 99 targets (38 packages loaded, 0 targets configured)
Analyzing: 99 targets (38 packages loaded, 0 targets configured)
[0 / 1] [Prepa] BazelWorkspaceStatusAction stable-status.txt
DEBUG: /private/var/tmp/_bazel_user/1426ad6c00f8f7b996ddc75bef70871c/external/rules_rust/bindgen/private/bindgen.bzl:280:14: WARN: rust_bindgen.leak_symbols is set to True for @//bindgen:simple_leaked_bindgen__bindgen - please file an issue at https://github.com/bazelbuild/rules_rust/issues explaining why this was necessary, as this support will be removed soon.
ERROR: /Users/user/Code/rules_rust/examples/bindgen/BUILD.bazel:4:21: in @@rules_rust//rust/private:rust_analyzer.bzl%rust_analyzer_aspect aspect on rust_library rule //bindgen:simple_bindgen:
Traceback (most recent call last):
	File "/private/var/tmp/_bazel_user/1426ad6c00f8f7b996ddc75bef70871c/external/rules_rust/rust/private/rust_analyzer.bzl", line 149, column 51, in _rust_analyzer_aspect_impl
		content = json.encode(_create_single_crate(ctx, rust_analyzer_info)),
	File "/private/var/tmp/_bazel_user/1426ad6c00f8f7b996ddc75bef70871c/external/rules_rust/rust/private/rust_analyzer.bzl", line 233, column 47, in _create_single_crate
		out_dir_path = info.build_info.out_dir.path
Error: 'NoneType' value has no field or method 'path'
ERROR: Analysis of aspects '[@@rules_rust//rust:defs.bzl%rust_analyzer_aspect] with parameters {} on //bindgen:simple_bindgen' failed; build aborted: Analysis of target '//bindgen:simple_bindgen' failed
INFO: Elapsed time: 0.552s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
ERROR: Build did NOT complete successfully

This change fixes this issue.

[daivinhtran]

Should you change the PR title to "Add CI Jobs for rust-analyzer rule" instead? I don't see any fix in the PR.