mavlink_stream: mutex lock for register/unregister poll #1474

Job	Run time
variables	1s
fc_matrix (pixhawk) / build	1m 45s
fc_matrix (fmu-v6xrt) / build	1m 16s
fc_matrix (saluki-nxp93_flat) / build	4m 10s
fc_matrix (saluki-pi_amp) / build	1m 24s
fc_matrix (saluki-pi_custom_keys, Tools/saluki-sec-scripts/custom_keys/saluki-pi/px4_bin_ed25519_... / build	1m 20s
fc_matrix (saluki-pi_default) / build	1m 17s
fc_matrix (saluki-pi_flat) / build	1m 17s
fc_matrix (saluki-v2_amp) / build	1m 35s
fc_matrix (saluki-v2_custom_keys, Tools/saluki-sec-scripts/custom_keys/saluki-v2/px4_bin_ed25519_... / build	1m 16s
fc_matrix (saluki-v2_flat) / build	1m 33s
fc_matrix (saluki-v2_default) / build	1m 34s
fc_matrix (saluki-v3_amp) / build	1m 17s
fc_matrix (saluki-v3_custom_keys, Tools/saluki-sec-scripts/custom_keys/saluki-v3/px4_bin_ed25519_... / build	1m 14s
fc_matrix (saluki-v3_default) / build	1m 33s
fc_matrix (saluki-v3_flat) / build	1m 43s
build px4fwupdater	0s
upload px4fwupdater to UAE docker registry	0s
upload px4fwupdater to docker registry	0s
upload builds to UAE artifactory	0s
	24m 15s

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