Fix(kclvm-codegen): fix schema back ref.

[zong-zhe]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

issue #231

2. What is the scope of this PR (e.g. component or file name):

kclvm-codegen

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

fix schema back reference exception.

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

6. Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[coveralls]

Pull Request Test Coverage Report for Build 3219451710

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 501 unchanged lines in 13 files lost coverage.
• Overall coverage decreased (-0.7%) to 57.494%

---

Files with Coverage Reduction	New Missed Lines	%
kclvm/3rdparty/rustc_span/src/source_map.rs	1	27.95%
kclvm/lexer/src/lib.rs	1	78.65%
kclvm/sema/src/ty/into.rs	1	78.33%
kclvm/sema/src/ty/unify.rs	1	93.91%
kclvm/parser/src/lexer/indent.rs	5	78.31%
kclvm/tools/src/vet/tests.rs	8	96.1%
kclvm/tools/src/vet/expr_builder.rs	9	95.26%
kclvm/3rdparty/rustc_span/src/analyze_source_file.rs	10	75.26%
kclvm/3rdparty/rustc_span/src/lib.rs	17	33.75%
kclvm/sema/src/ty/mod.rs	35	66.02%

Totals
Change from base Build 3213156415:	-0.7%
Covered Lines:	19379
Relevant Lines:	33706

---

💛 - Coveralls

[Peefy]

LGTM

[chai2010]

LGTM