Temporarily disable tests permanently failing on 10.5

This are filed as issues so I trust these will not be forgotten:
- MDEV-20372
- MDEV-21965
- MDEV-21968
- MDEV-22119

Having these tests fail the MTR permanently decreases the overall quality
of the software as:
- developers start neglecting the results from CI systems and do not spot
  the new regressions their changes introduce
- reviews take many hours as a diligent reviewer needs to open all build
  logs that are failing, see what is failing, and check if those are new
  failures or not – alternatively reviewers stop looking at CI altogether

It is better to disable these test now and prioritize the MDEVs for the
test failure bugs than keep the MTR red and allow more test failures to
creep in.

mysql-test/unstable-tests

@@ -78,6 +78,7 @@ main.host_cache_size_functionality    : MDEV-10606 - sporadic failure on shutdow
 main.index_intersect_innodb           : MDEV-10643 - failed with timeout
 main.index_merge_innodb               : MDEV-7142 - Plan mismatch
 main.innodb_icp                       : MDEV-20168 - Wrong execution plans
+main.innodb_ext_key                   : MDEV-22119 - fails with NULL values
 main.innodb_mysql_lock                : MDEV-7861 - Wrong result
 main.insert_debug                     : Added in 10.4.12
 main.ipv4_and_ipv6                    : MDEV-20964 - Wrong result
@@ -172,7 +173,10 @@ main.status                           : MDEV-13255 - Wrong result
 main.subselect                        : MDEV-20551 - Valgrind failure
 main.subselect_innodb                 : MDEV-10614 - Wrong result
 main.tc_heuristic_recover             : MDEV-14189 - Wrong result
+main.thread_pool_info                 : MDEV-20372 - thread_pool_info fails randomly in 10.5
 main.timezone2                        : Modified in 10.4.12
+main.tls_version                      : MDEV-21965 - old TLS versions don't work on latest Debian and Ubuntu releases
+main.tls_version1                     : MDEV-21965 - old TLS versions don't work on latest Debian and Ubuntu releases
 main.type_blob                        : MDEV-15195 - Wrong result
 main.type_datetime                    : Modified in 10.4.12
 main.type_datetime_hires              : MDEV-10687 - Timeout
@@ -188,6 +192,7 @@ main.wait_timeout                     : MDEV-19023 - Lost connection to MySQL se
 main.warnings_debug                   : Modified in 10.4.12
 main.win                              : Modified in 10.4.12
 main.xa                               : MDEV-11769 - lock wait timeout
+main.xml                              : MDEV-21968 - mysql crashes on test main.xml on arch armhf
 
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