Bump springdoc-openapi-webmvc-core version to ensure spring-webmvc exceeds v5.3.18

[autumnust]

Summary

It turns out that forcing is not necessary as Gradle is smart enough to pick the higher version when there are both 5.3.13 and 5.3.18 of org.springframework:spring-webmvc appeared. However this doesn't prohibit the version 5.3.13 itself being present in the resolution tree. Thus when dependency tree is resolved, the version 5.3.13 will still cause security vulnerability.

This change is eliminate the presence of 5.3.13 from the source. org.springdoc:springdoc-openapi-ui:1.6.9 is depending on 5.3.20 of org.springframework:spring-webmvc

Issue] Briefly discuss the summary of the changes made in this
pull request in 2-3 lines.

Changes

• Client-facing API Changes
• Internal API Changes
• Bug Fixes
• New Features
• Performance Improvements
• Code Style
• Refactoring
• Documentation
• Tests

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Testing

• Manually Tested on local docker setup. Please include commands ran, and their output.
• Added new tests for the changes made.
• Updated existing tests to reflect the changes made.
• No tests added or updated. Please explain why. If unsure, please feel free to ask for help.
• Some other form of testing like staging or soak time in production. Please explain.

See the dependency tree updated below

|    +--- org.springdoc:springdoc-openapi-webmvc-core:1.6.9
|    |    +--- org.springdoc:springdoc-openapi-common:1.6.9
|    |    |    +--- org.springframework.boot:spring-boot-autoconfigure:2.7.0 -> 2.7.11 (*)
|    |    |    +--- org.springframework:spring-web:5.3.20 (*)
|    |    |    \--- io.swagger.core.v3:swagger-core:2.2.0
|    |    |         +--- jakarta.xml.bind:jakarta.xml.bind-api:2.3.2
|    |    |         |    \--- jakarta.activation:jakarta.activation-api:1.2.1
|    |    |         +--- org.apache.commons:commons-lang3:3.12.0
|    |    |         +--- org.slf4j:slf4j-api:1.7.35 -> 1.7.36
|    |    |         +--- com.fasterxml.jackson.core:jackson-annotations:2.13.2 -> 2.13.4 (*)
|    |    |         +--- com.fasterxml.jackson.core:jackson-databind:2.13.2.2 -> 2.13.4 (*)
|    |    |         +--- com.fasterxml.jackson.dataformat:jackson-dataformat-yaml:2.13.2 -> 2.13.4
|    |    |         |    +--- com.fasterxml.jackson.core:jackson-databind:2.13.4 (*)
|    |    |         |    +--- org.yaml:snakeyaml:1.31
|    |    |         |    +--- com.fasterxml.jackson.core:jackson-core:2.13.4 (*)
|    |    |         |    \--- com.fasterxml.jackson:jackson-bom:2.13.4 (*)
|    |    |         +--- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:2.13.2 -> 2.13.4 (*)
|    |    |         +--- io.swagger.core.v3:swagger-annotations:2.2.0
|    |    |         +--- io.swagger.core.v3:swagger-models:2.2.0
|    |    |         |    \--- com.fasterxml.jackson.core:jackson-annotations:2.13.2 -> 2.13.4 (*)
|    |    |         \--- jakarta.validation:jakarta.validation-api:2.0.2
|    |    \--- org.springframework:spring-webmvc:5.3.20 (*)

For all the boxes checked, include a detailed description of the testing done for the changes made in this pull request.

Additional Information

• Breaking Changes
• Deprecations
• Large PR broken into smaller PRs, and PR plan linked in the description.

For all the boxes checked, include additional details of the changes made in this pull request.