Set maven version requirement to 3.6.3

[Abacn]

In alignment with https://github.com/apache/maven-plugin-tools/blob/maven-plugin-tools-3.15.1/maven-plugin-plugin/pom.xml#L38

as we bumped maven-plugin plugin to 3.15.1 in #2050

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 46.74%. Comparing base (a2779d4) to head (e56d324).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2142      +/-   ##
============================================
- Coverage     46.74%   46.74%   -0.01%     
+ Complexity     3977     3976       -1     
============================================
  Files           873      873              
  Lines         51871    51871              
  Branches       5429     5429              
============================================
- Hits          24248    24247       -1     
  Misses        25897    25897              
- Partials       1726     1727       +1     

Components	Coverage Δ
spanner-templates	68.63% <ø> (-0.01%)	⬇️
spanner-import-export	65.57% <ø> (-0.02%)	⬇️
spanner-live-forward-migration	76.49% <ø> (ø)
spanner-live-reverse-replication	78.39% <ø> (ø)
spanner-bulk-migration	87.87% <ø> (ø)

see 1 file with indirect coverage changes

[liferoad]

This happened before (https://github.com/GoogleCloudPlatform/DataflowTemplates/actions/runs/12877500595), which should not be caused by this PR.

2025-01-21 23:28:09 5.14.0 WARNING Failed to get OTEL, will skip exporting client side metrics 
java.lang.NoClassDefFoundError: io/opentelemetry/api/incubator/trace/ExtendedTracer
	at io.opentelemetry.sdk.trace.SdkTracerProvider.<init>(SdkTracerProvider.java:56)
	at io.opentelemetry.sdk.trace.SdkTracerProviderBuilder.build(SdkTracerProviderBuilder.java:212)
	at io.opentelemetry.sdk.OpenTelemetrySdkBuilder.build(OpenTelemetrySdkBuilder.java:101)
	at com.google.cloud.bigtable.data.v2.stub.metrics.DefaultMetricsProvider.getOpenTelemetry(DefaultMetricsProvider.java:51)
	at com.google.cloud.bigtable.data.v2.stub.EnhancedBigtableStub.getOpenTelemetry(EnhancedBigtableStub.java:393)
	at com.google.cloud.bigtable.data.v2.stub.EnhancedBigtableStub.create(EnhancedBigtableStub.java:223)
	at com.google.cloud.bigtable.data.v2.stub.BigtableChannelPrimer.sendPrimeRequests(BigtableChannelPrimer.java:90)
	at com.google.cloud.bigtable.data.v2.stub.BigtableChannelPrimer.primeChannelUnsafe(BigtableChannelPrimer.java:78)
	at com.google.cloud.bigtable.data.v2.stub.BigtableChannelPrimer.primeChannel(BigtableChannelPrimer.java:70)
	at com.google.api.gax.grpc.InstantiatingGrpcChannelProvider.createSingleChannel(InstantiatingGrpcChannelProvider.java:444)
	```

[Abacn]

CassandraToBigtableIT failed not related to the change. merging for now.