chore(deps): update dependency net.logstash.logback:logstash-logback-encoder to v7.4

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
net.logstash.logback:logstash-logback-encoder	7.0.1 -> 7.4

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[diegomarquezp]

Error:  COMPILATION ERROR : 
[INFO] -------------------------------------------------------------
Error:  /home/runner/work/spring-cloud-gcp/spring-cloud-gcp/spring-cloud-gcp-logging/src/main/java/com/google/cloud/spring/logging/extensions/LogstashLoggingEventEnhancer.java:[46,64] error: getFieldValue() has protected access in ObjectAppendingMarker
Error:  /home/runner/work/spring-cloud-gcp/spring-cloud-gcp/spring-cloud-gcp-logging/src/main/java/com/google/cloud/spring/logging/extensions/LogstashLoggingEventEnhancer.java:[53,59] error: getFieldValue() has protected access in ObjectAppendingMarker

[diegomarquezp]

tracked in #1764

[diegomarquezp]

Opened an issue logfellow/logstash-logback-encoder#991