snmp_exporter: update to 0.26.0.

## 0.26.0 / 2024-05-08

* [CHANGE] Improve generator parse error handling #1167
* [ENHANCEMENT] generator: Add generator HELP override #1106
* [ENHANCEMENT] Refactoring of Scrape process, fixing multiple module issues #1111
* [ENHANCEMENT] Skip using an interactive terminal in "make docker-generate". #1113
* [ENHANCEMENT] Add SNMPInflight metric #1119
* [FEATURE] Support for passing username, password & priv_password as env vars #1074
* [FEATURE] Add GoSNMP logger #1157
* [FEATURE] Add a "snmp_context" parameter to the URL #1163
* [BUGFIX] generator: curl failed #1094
* [BUGFIX] Fix SNMPv3 password configuration #1122
* [BUGFIX] generator: Update generator User-Agent #1133
* [BUGFIX] generator: fix mibs directory specification for parse_errors command #1135
* [BUGFIX] generator: remove extra character from dell iDrac-SMIv1 MIB #1141
* [BUGFIX] Fix do not expand envvars for empty config fields #1148

snmp.yml changes:
* Updated Cisco MIBs #1180
* Updated Cyberpower MIBs #1124
* Updated servertech_sentry3 #1090
* Added support for Dell iDrac  #1125

(wiz)