The ornamental design for an air-filter mounting bracket, as shown.
FIG. 1 is a top perspective view of an air-filter mounting bracket, showing my new design;
FIG. 2 is a front side elevation view thereof;
FIG. 3 is a back side elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a top perspective view of two such air-filter mounting brackets, shown in an example environment mounting an air filter to a fan.
The broken lines showing an example air filter and an example fan illustrate example environmental structure, are not part of the design sought to be patented, and form no part of the claimed design.