fix: fix ty error in assignment

[zong-zhe]

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

• N
• Y

Fixed #821

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

kclvm/sema/src/resolver/node.rs

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

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

[coveralls]

Pull Request Test Coverage Report for Build 6939919112

• 26 of 26 (100.0%) changed or added relevant lines in 2 files are covered.
• 471 unchanged lines in 8 files lost coverage.
• Overall coverage decreased (-15.7%) to 72.074%

---

Files with Coverage Reduction	New Missed Lines	%
compiler_base/error/src/diagnostic/components.rs	6	0.0%
compiler_base/error/src/errors.rs	8	0.0%
compiler_base/session/src/lib.rs	26	58.06%
compiler_base/error/src/diagnostic/mod.rs	27	0.0%
compiler_base/error/src/diagnostic/style.rs	41	0.0%
compiler_base/error/src/diagnostic/diagnostic_message.rs	74	0.0%
compiler_base/error/src/emitter.rs	119	0.0%
compiler_base/error/src/diagnostic/diagnostic_handler.rs	170	0.0%

Totals
Change from base Build 6938416596:	-15.7%
Covered Lines:	41643
Relevant Lines:	57778

---

💛 - Coveralls

[Peefy]

LGTM