DRIVERS-2768 skip search index tests on 7.1

[kevinAlbs]

Summary

Follow-up to #1541

Skip search index tests on server 7.1.

Background & Motivation

This PR is intended to fix failing tests in the C driver using server version 7.1.0 (latest available on Ubuntu 18.04). An example failure logs:

expected error to contain "Atlas", but got: "BSON field 'createSearchIndexes.indexes.type' is an unknown field."

The "unknown field" error message appears in server 7.1.0, but not 7.0.9 or 7.2.1:

With 7.0.5:

% mongosh --eval "print(db.version()); db.runCommand({createSearchIndexes: 'coll', indexes: [{definition: { mappings: { dynamic: true } }, type: 'search' }]});"
7.0.5
MongoServerError: Search index commands are only supported with Atlas.

With 7.1.0:

% mongosh --eval "print(db.version()); db.runCommand({createSearchIndexes: 'coll', indexes: [{definition: { mappings: { dynamic: true } }, type: 'search' }]});"
7.1.0
MongoServerError: BSON field 'createSearchIndexes.indexes.type' is an unknown field.

With 7.2.1:

% mongosh --eval "print(db.version()); db.runCommand({createSearchIndexes: 'coll', indexes: [{definition: { mappings: { dynamic: true } }, type: 'search' }]});"
7.2.1
MongoServerError: Search index commands are only supported with Atlas.

I expect this is because SERVER-83107 was backported to 7.0.5 and 7.2.1, but not to a 7.1 version.

Please complete the following before merging:

• [ ] Update changelog. Not applicable. Test changes only.
• Make sure there are generated JSON files from the YAML test files.
• Test changes in at least one language driver.
• Test these changes against all server versions and topologies (including standalone, replica set, sharded
  clusters, and serverless).

[jmikola]

@kevinAlbs: Was this change only necessary because libmongoc is always sending a value for the type option? I'm specifically curious about the change to searchIndexIgnoresReadWriteConcern.yml since the file was never even modified in @NoahStapp's original commit (39db05c).

While restoring the missing spec documentation in #1650, I clarified that the server applies its own defaults for type and name if they're not specified by the driver. I didn't see any reason for a driver to explicitly apply its own default value(s).

[kevinAlbs]

@kevinAlbs: Was this change only necessary because libmongoc is always sending a value for the type option?

No, libmongoc is only passing type for tests that specify.

I'm specifically curious about the change to searchIndexIgnoresReadWriteConcern.yml

My mistake. searchIndexIgnoresReadWriteConcern.yml does not specify a type. Submitted #1651 to revert changes to that file.